The second world war is the most popular period for alternate histories. This page is a list of possible points of divergence during and before the second world war, along with some suggested consequences. Basically, it's about sixty alternate history essays, each about one paragraph long.
This document is intended as a very broad-brush discussion of the field, which others can use as a foundation for more detailed alternate histories. You'll need to do a lot of research, and in the process you'll likely find out I was talking nonsense about half the time. If you choose to write up one of these then please drop me a line. The times during World War Two discussed below are the times of important consequences: the most elegant choice of a point of divergence may be earlier.
The piece of Germany on the left bank of the Rhine had been kept demilitarised since the end of the first world war. Moving troops in was arguably the first thing Hitler did that flaunted its inconsistency with the Versailles treaty. What if France had decided to respond with force? Germany didn't have an army capable of fighting France, and would have had to back down. Would the blow to Hitler's prestige be sufficient to topple him? Would France's name be mud in all peace-loving countries? The point of divergence would have to create a lot more political will in France, or at least a lot more anti-German feeling.
Stalin had several purges, but I'm talking about the one in the late 1930s. It was a key reason why the Soviet Union's army put up such a poor showing in the Winter War with Finland and the weeks after Barbarossa.
Case I: The purge doesn't happen: The army will be stronger. Tukachevsky, a brilliant theorist and field commander, will still be alive: he may end up in the job that Zhukov had historically.
Case II: The purge is worse: The army will be weaker: maybe weak enough that they lose. Zhukov joins Tukachevsky in an unmarked grave. Morons may command the Red Army.
Case III: Stalin's enemies depose him: Just because Stalin was paranoid doesn't mean nobody was out to get him. Let's imagine that without the purge there would have been a coup of Red Army generals and politburo political enemies. The new leader might be Tukachevsky, Zhukov, or one of Stalin's political enemies.
German annexation of Austria was popular in both countries. It's hard to see who would intervene to stop it, though Mussolini had in 1934. When asked why he didn't intervene the second time, he said that in 1934 he would have won. If the war starts over this there'll be a lot of anti-war sentiment in the west.
The Sudetenland was a mountainous border region of what's now the Czech Republic, mostly populated by Germans (it might be better to think of them as Austrians). Nationalist principles implied that they should be joined to Germany. But if they were, Czechoslovakia would become indefensible: the Sudetenland had the best defensive terrain, a lot of smokestack industries and the Czech version of the Maginot line. Historically, Czechoslovakia was forced to give them up because France and Britain wouldn't back them up and they couldn't beat Germany on their own.
Case I: France and Britain back Czechoslovakia: Hitler probably would have had to back down: Germany wasn't ready for war yet.
Case II: Poland backs Czechoslovakia: Historically, Poland acquiesced in the dismemberment of their only nearby natural ally in return for the town of Teschen. A seriously bad bargain. But by the standards of 1938 Poland and Czechoslovakia together have a pretty good army. Even without a western declaration of war they may just be able to force the Germans to back down: especially if great power intervention (from the west or the east) is always a possibility.
Case III: Poland, France and Britain back Czechoslovakia: Hitler definitely has to back down.
Case IV: The USSR and Poland back Czechoslovakia: This assumes Poland at least allows the USSR to rail troops and supplies across Polish territory. Not sure how plausible it is, or what the result would be. You can think of this as Poland jumping at a chance to let Russia and Germany fight somewhere that isn't Poland. I don't see that Russian soldiers locked into railway cars, by the way, are a security threat to Poland.
Germany occupied what was left of Czechoslovakia too fast for anyone to do anything about it. The action gave Germany a big increase in its military strength: a third of the tanks that attacked France in 1940 were made in Czechoslovakia (before or after the conquest). But the action cost Germany a lot diplomatically: this is arguably the first time Germany did something for which it had no real excuse, and it made it clear that Hitler could not be trusted. As a result, it's the last major piece of intimidatory expansion Hitler got away with.
I doubt there's much of a point of divergence here, unless it's Germany not occupying the rump. Which requires a different approach to diplomacy on Hitler's part: he doesn't seem to have realised that the western powers took the Munich agreement seriously.
One of the USSR's aims seems to have been to recover the territory lost in the collapse of the Russian Empire, and Poland holds a lot. Edward Stasiak suggests an August 1936 trigger. As a general remark, the earlier the war happens the better chance the minor country has: major powers like Russia, Germany, France, Britain and Italy mostly built up their militaries much faster than the minor powers could.
Germany's immediate claim was on the so-called Polish corridor, around Danzig, but in the long run Poland had to fight or surrender. What if Poland had given up the corridor and become a German minion? It's not crazy: fear of Russia could be a motive, and realistically the Poles had missed their best chance to resist a year ago when they let the Czechs be devoured. Surrender removes the trigger for a western entry into the war (see below) and it creates a border between the Third Reich and the Soviet Union. A war between them may follow, since it's much closer to what Hitler wants than a war with the west, and Poland will fight as a German ally. Certainly Russia will react to the appearance of the Wehrmacht in Poland with fear and loathing. The Baltic States now become interesting, and a good trigger for the Russo-German war. Who would win that war is very hard to guess.
Hitler thought they wouldn't. After all, what sort of idiot would let powerful, well-defended democratic Czechoslovakia be destroyed without a fight, then fight to defend the militarily and morally indefensible military dictatorship of Poland?
What if Hitler had been right? Poland is rapidly demolished, and whatever parts of Eastern Europe haven't fallen into the German or Soviet camps do so swiftly. War between Germany and the Soviet Union is then likely, to general western schadenfreude.
After and during the fall of Poland, France and Britain remained almost entirely passive, despite facing a very weak German garrison. What if they'd taken the offensive?
Case I: Across the Franco-German border: Not much of a frontage, and straight into the Siegfried line. I don't think France has the strength to get anywhere, though it was probably worth a try.
Case II: By Invitation Through Belgium: I don't know what it would take to make Belgium join the allies. This offensive might get somewhere, though I'm sceptical it would bring down Germany.
Case III: By Invasion Through Belgium: I can't see this happening: if it does, the France and Britain will look very bad indeed. Perhaps if we assume the Belgians had done some deal with the Germans beforehand?
This was a revanchist land grab (Finland had been part of the pre-revolutionary Russian Empire) by the USSR against Finland. Finland did very well, or the USSR did very badly, depending on your point of view. But eventually the USSR's huge numerical advantage ground the Finns down, and Finland had to make peace by giving up a larger chunk of border land than the original Russian demand. The war motivated Finland to make a vague and desultory attack on the USSR alongside Germany: they wanted the stolen territory back, but never really had their heart in an attempt to destroy the USSR. When the tide turned against Germany, Finland shrugged, gave the territory back up, and made a separate peace.
Case I: Finland wins: Stalin gets bored with attacking Finland and makes some face-saving deal. Finland presumably never enters the war. This is a POD of interest to Finns, but probably of little impact on the big picture.
Case II: It never happens: Stalin doesn't attack. He may go and do something else violent instead. Otherwise, neither Germany nor Stalin finds out just how awful the Red Army is. It's arguable that this reduces the chance of Barbarossa happening, or even of a Russo-German war of any kind happening. On the other hand, if there is a Russo-German war the Germans are likely to do very well, because nobody's been fixing all the things that are wrong with the Red Army. Finland won't be involved, even to the limited extent it was historically.
Case III: Finland surrenders quickly: Finland realises it can't win, so it doesn't fight. Russia takes a slice of territory, not as much as historically. And Finland will have a grudge. Otherwise it's just like Case II.
Case IV: Finland gets steamrolled: Deprive Finland of Mannerheim's leadership, make a few other adjustments, and assume they have some bad luck. Finland is rapidly and cheaply defeated. Everybody thinks the Russian army pretty competent. Finland attacks Russia in Barbarossa, and recovers the territory. When (if) the war turns against Germany, Finland tries to make peace. But the Russians have no great respect for Finnish skill at arms and decide to make a finish of it (no pun intended). Post-war Finland is just another Eastern European satellite with a communist government. Sweden finds itself on the front line and perhaps joins the NATO analogue.
Case V: The allies support Finland: I don't know how to make this happen, but it was talked about. This brings the USSR in as an active ally of Germany, at least for a while. I don't know how the allies get there but they'll probably be talking to Norway and Sweden, as well as directly landing at Petsamo.
Historically Norway was invaded almost simultaneously by Germany and Britain: each saw it as important, each feared (rightly) that the other would attack and each (rightly) thought the Norwegians incapable of defending themselves. Germany also overrun Denmark in the process of getting to Norway. The main reason was the iron ore shipments that run (at least part of the year) from Kiruna in Sweden by rail to Narvik in Norway, then down the coast to German ports. By being fractionally later, the allies got the diplomatic credit for defending Norway rather than attacking it.
Case I: No invasion: Germany lost half its navy in the Norwegian campaign, that won't happen. Various British losses won't happen either but I'm not sure of their importance.
Case II: The allies attack first: The allies look like bullies, that may affect American support. The allies may do slightly better in the fighting but probably not much.
Case III: The allies get bogged down: The saving grace for the allies was that Norway was all over quickly. If the commitment had been more severe that could have an effect on the battle for France.
There were three sectors to the French-German effective border: a southern sector covered by the Maginot line; a central sector that the French thought impenetrable due to the Ardennes forest; and a northern sector where the French expected to be attacked and massed their best armies. The French plan was to advance through the northern sector to save as much of Belgium as possible. The Germans attacked through the centre, demonstrating that the Ardennes were not impassable after all. This left the bulk of the French army hopelessly outflanked and rapidly pocketed, and led to a swift German victory. Almost any POD gives the French a better chance than what happened historically.
Case I: Germans attack in the north: They were planning to do this, but changed their minds at the last minute, partly because the plans fell into allied hands. This leads to a German attack straight into the teeth of the French defence: the best case the French can possibly hope for, even so I'm not sure they will win.
Case II: Germany and France both concentrate in the centre: This probably requires an intelligence leak, perhaps an intercept decoded by the British. Same comments apply, if anything this is better for France since the forest will favour the defence.
Case III: Belgium joins the allies: Belgium remained neutral, but surely understood that Germany was the main threat. If Belgium concludes it's for the chop in any case it may agree to allow French and British troops to enter its territory: say, during the phoney war. That changes the campaign a lot and I'd only be guessing if I said how. Once again, it's hardly likely to be worse than history.
What if the Anglo-French armies trying to evacuate from Dunkirk get wiped out? Deprived of this core the British army will lack the cadres needed to train new recruits. As a result its army will be of much lower quality throughout the war, a bit like it was in the first world war after its expeditionary force was wiped out in August 1914.
Vichy France was set up by the Germans to neutralise French resistance and hopefully produce an ally. The territories of France tended to sign up to the Vichy government unless they were immediately exposed to allied pressure (e.g. New Caledonia). In practice the only significant achievement of the Vichy French armed forces was to defeat an allied attack on Senegal, in West Africa. In 1942 it became clear that the Vichy French could not be relied upon to achieve anything for the German cause, and Hitler ended the farce, occupying the Vichy part of the country as the allies rolled up North Africa.
Case I: Active French participation in axis: There was some anti-British feeling on the part of the French, partly due to the British attack on French fleet elements they feared would fall into German hands. Suppose France was even more irritated with Britain for some reason. French troops could help to bolster Germany in the east, the way Rumanians, Hungarians etc. did historically. The SS will also recruit more successfully from France. The French navy becomes available to the Germans, except for whatever the British have already sunk.
Case II: Stronger Free France: Suppose Vichy France is seen by the French with contempt. Perhaps Petain refusing to support it would be an aspect of the POD. The most important areas are Senegal, Northwest Africa and Syria. If all these go Free French then all of Africa will fall rapidly.
This could go differently, but I'm not sure what the impact would be. Worst case for Britain is that the fighters get driven out of Southern England and the Germans pound London and the southern cities with impunity. For a while, at least.
The German invasion of Britain. Others have written as to why this could never work. Strictly, of course, that's a meaningless statement in alternate history. Let's rephrase by saying that the point of divergence required to make Sea Lion possible will be so large and/or early that the alternate history resulting will be too different from real history to justify using the same name.
If you're determined anyway, you'll need every POD you can scrape up. Have the bulk of the Danish, Norwegian, Dutch and French navies fall intact into German hands, preferably with their crews carrying grudges against perfidious Albion. Chop the British navy up in an invasion of Norway or something. Wipe out the British army: Dunkirk is a popular place for that. Inflict much higher losses on the Royal Air Force during the fall of France. Have the Germans see the attack on Britain not as a separate campaign but as a natural continuation of the defeat of France, and have them draw up the plans before they even attack France. Let the Germans have a clever idea as to how to get the troops across: something to supplement the Elbe-Rhine barge fleet. Let the British make a bad mistake when guessing where they'll land: they did historically. Give the Germans some experience (off Norway?) bombing ships, so they get good at it. Transfer the best of the Regia Aeronautica to the channel to assist the Luftwaffe. Best of luck, you'll need it.
Franco liked to say that he fought as a German ally on the eastern front of the European war, as an American ally in the Pacific, and stayed neutral in the west. Spain traded with Germany from the fall of France until late in the war.
Case I: Spanish Republicans win unassisted: They'll be friendly to the USSR, which means they will trade with the Germans from the fall of France to Barbarossa, then cut off relations. Unless invaded by the Germans they will offer themselves as a launching platform for the second front. If they are invaded then Britain gets to fight a twentieth century version of the Napoleonic peninsular war.
Case II: Spanish Republicans win with Russian assistance: As Case I, but more so.
Case III: Spanish Republicans win with western assistance: Spain may fight on the allied side in the war. But perhaps not, they are tired of fighting and still more aligned with the USSR than the west.
Case IV: Spanish civil war drags on: What if the Spanish civil war were still in progress when France declared war on Germany? There's a German army of "volunteers" fighting alongside Franco. Spain would become the first theatre of war in the west.
Case V: Spain allies with Germany: Say, just after the fall of France. Historically Spain demanded so much as its price that Hitler said forget it. Germany can use Spain as a launching pad to attack Gibraltar and close one end of the Mediterranean. The loss of Gibraltar and Spain would make it very hard for the allies to take the offensive in North Africa, to carry out operations like Torch, or later to land in Italy. So the landings aimed at the liberation of France move up to 1943.
Case VI: Germany invades Spain: Would Franco really fight the Germans, when he has the chance to acquiesce? I assume the Germans win, and Spain becomes even more devastated. But it may not be pleasant, peninsulas with tough terrain and poor transport infrastructure, like Spain, are vulnerable to allied sea power.
Turkey stayed out of the war and traded with Germany until very near the end, when it made a token declaration.
Case I: Turkey as a German victim: Same comments apply as to Spain. Idea is for Germany to directly threaten the Caucasus. It also gives the axis control of the Bosphorus-Dardanelles but I'm not sure that's important. I'm not sure I really believe this idea.
Case II: Turkey as a German ally: As above, but no need for an invasion and the Turkish army as an ally. Turkey can influence events in the Caucasus, Syria, Iraq, maybe Greece.
The Soviet Union did have a plan for this, one was drawn up by Zhukov. It was sort of like a larger version of the German invasion of France, pushing through the centre then hooking north to pocket Army Group North (to borrow a term from Barbarossa) against the Baltic. Who knows how well it would have worked: probably not really well, but also probably better than Barbarossa was for the Russians. The two obvious times are early 1941 and mid-1940. The latter is probably more interesting. Either way the Russians will have struck first, which increases the chance the Russian people will blame Stalin for the war. The Russian buildup during 1940 was huge, so both sides will be weaker in numerical terms.
The German attack on Yugoslavia and Greece may have delayed Barbarossa. Or may not, depending on who you believe about the weather. It certainly diverted British troops from North Africa, letting Rommel achieve impressive things. The root POD here may be the Italian attack on Greece.
Always a good subject for debate. Barbarossa was a brilliant tactical success, though it didn't quite achieve its optimistic objectives. In the long run, of course, it was a strategic catastrophe for Germany. A key question is whether Germany had a choice: would the USSR have attacked eventually anyway?
Case I: It doesn't happen: This leaves Germany facing a powerful but quiescent USSR in the east, and a belligerent but largely helpless Britain in the west. When and if the US enters the war the allies can probably win the Battle of the Atlantic, but it's going to be a terrible drain: every unit of resources allocated by Germany to submarines requires far more allocated by the west to anti-submarine warfare and replacement of shipping losses. The allies can't kick Germany out of France, or knock Italy out of the war, without Russia taking the brunt of the fighting. The three possibilities obviously worth looking at here are: a negotiated peace in the west; an eventual USSR attack on Germany; and the development and use of nuclear fission bombs by one or both sides.
Case I: Germany does better: Just having the Germans prepare better
Case I: USSR does better: Easy to arrange, just let Stalin listen to a few of the warnings he historically ignored. It's not clear it's a very interesting POD, though. The war will presumably be shorter, and Russia less exhausted, perhaps the USSR will control more of Europe.
Case II: Single main objective: Some thinkers have attacked Barbarossa as being unfocused. Each army group had a separate objective: Leningrad in the north, Moscow in the centre and Stalingrad in the south. There are some what-ifs you can play here assuming that the Germans identify one of these as the Russian centre of gravity, the most popular choice being Moscow. This isn't an easy plausibility argument, if you want to start from a small have a good grasp of military logistics.
Japan attacked Russia in 1939 and had the dreadful bad luck to run into a Russian general called Zhukov. (Who'd been exiled there by Stalin in order to put him on tenure track for a gulag and an execution, so if you stop Zhukov's arrest there'll be someone else in the theatre. This makes Zhukov's arrest a rather elegant POD.) The result was a modest but quite dramatic Japanese defeat at Nomonhan. POD that away and the Japanese may be willing to attack the USSR in alliance with the Germans. They probably won't do all that well, they really never did against European armies except in jungles. But the distraction could be very serious, and the lend lease that historically flowed on Russian ships from America to Vladivostok will cease.
Life in Stalin's idea of a socialist Utopia wasn't fun. So when the Germans arrived in places like the Ukraine they were initially hailed as liberators by a significant percentage of the population. By their nature, however, nazis cannot be put in contact with Slavs without a high risk of massacre. The Third Reich rapidly ran through its fund of good will and achieved an amazing thing: turned the Ukrainians into supporters of Russia. Changing this will take a big POD: racist brutality isn't a detachable aspect of nazism, it's a central element. But letting the Germans keep a few friends would go some way toward any German victory scenario you wanted to construct. Ironically, the big winner from the change would be the SS, which could recruit Ukrainians, etc.; yet the SS is the historical worst offender.
The Germans diverted significant resources into killing people they didn't really need to. Jews are the famous example, but Gipsies, educated Poles, commissars, etc. are all worth remembering as well. (Apologies for anyone I left out, but that just underlines the point that this document is intended as a brief outline.) A Germany that harnessed those people's talents would be really scary, but that's probably too much to hope. (When I say hope, of course, what I really mean is fear.) A Germany that just used them as brute slaves might at least be slightly more efficient. The most interesting consequences might be in having all those educated, creative people still alive after the war. Add four million or so Jews, still alive and mostly wanting to leave Europe, and see what Israel turns into, or New York.
The Japanese felt themselves forced into war with the US, because their oil supplies had been cut off. This was the result of a sort of accidental diplomatic blockade: the US cut off their oil to protest Japanese occupation of French Indochina, and the Dutch and British cut off theirs because they thought it would please the Americans. It doesn't seem the Americans wanted to hurt the Japanese quite as badly as they did. American terms for a resumption of oil supplies were withdrawal from China. Nobody in Japan knew whether meant just China south of the great wall, which they might be willing to do, or Manchuria and/or Taiwan as well, which they wouldn't. There are plenty of PODs here for keeping Japan out of the war. The post-war implications of a powerful nationalist state in East Asia are fascinating.
After Pearl Harbour Japan rampaged across the western Pacific for six months. Something that should be made clear: Japan can't win against a serious America. Historically the US crushed Japan using about a fifth of its strength, the rest going to Europe. Make Japan tougher and you just force the US to allocate a little more or take a little longer. If you want Japan to win it has to be mostly a political change.
Case I: It doesn't happen: It was always a risky plan, so let's assume it never happened. The old American battleships survive, which is a mixed blessing because they're too slow to keep up with the carrier fleet. The Japanese carriers that struck Hawaii are off doing other things and so Japanese expansion goes a little faster.
Case II: The carriers are sunk: This could make a big dent in the American response. Japan's rampage will last significantly longer. American counterattacks will have to wait for the Essex-class carriers, but maybe Japan will have pushed further out by the time they come. Which won't clearly be good news for Japan.
Case III: The fuel supplies are wiped out: This will slow the Americans down a lot, but I doubt the implications are very interesting. Ships will go to Europe instead, which will help the Atlantic war.
Case IV: The carriers are spotted: A battle at sea follows, which the Japanese almost certainly win. Ships that get sunk in this battle won't rest on the bottom of the harbour waiting for salvage: they're gone for good.
Hitler underestimated the United States in particular and the importance of convertible civilian industry in general. He may also have overestimated the long term importance of Operation Drumbeat, the mugging of a hopelessly ill-prepared US merchant fleet by U-boats. And he probably figured that with the US and Britain cooperating closely in the Pacific against Japan, they would also cooperate closely in the Atlantic. Even so, gratuitously delaring war on the United States was the action of a loon.
So what if he doesn't? FDR is going to find it hard to ask for a declaration of war against Germany, now that the US has a real live actively evil empire to fight and no desire for distractions. He'll have to sell it by claiming the axis is a real alliance, but will congress believe him? Hitler can make that especially hard through speeches declaring solidarity with the Aryan people of America. In fact, a declaration of war on the Empire of Japan would cost very little and is probably worth every pfennig's worth of ink in the pen he uses. And why not go the whole hog: offer the United States the services of, say, a brigade of German volunteers (they may even actually have volunteered!). The eastern front will never notice the loss of a single brigade, and even when the US turns the offer down it's all ammunition to the "Japan first!" crowd in congress. If you want to contemplate some less plausible options, what if the US says yes? Then there'll be US soldiers serving alongside Wehrmacht: improving US doctrine, building personal links and making the US army realise that these guys are really capable and really evil. Germany may ask the American congress to send over that Joe Kennedy chap to help mediate peace between Germany and Britain. Sound fellow.
In my opinion, the pivotal moment of the war. German forces reached the outskirts of Moscow, and advanced elements even circled behind it to cut rail lines. Historically a Russian counteroffensive drove the Germans back, but what if the Germans had taken Moscow? This is an enormous blow to the USSR: the loss of Moscow's industry; its importance as a transportation hub; the disruption to war planning; and morale. Comrade Stalin might just find himself up against a wall in front of a firing squad, with the new government making whatever deal they can. It isn't easy to take a city that's stubbornly defended, so we're looking for a POD that worsens the Russian's historical level of surprise.
The American victory at Midway ended the historical Japanese rampage. The attack was partially triggered by the Doolittle raid, so that's a possible POD.
Case I: No attempt: The Japanese are obviously stronger. The Americans will have to kill their fleet honestly. Which they will, by overwhelming force. But not before the Essex-class carriers arrive.
Case II: The US doesn't respond: Perhaps because the Japanese change their codes. Midway falls, and the US will have to respond somehow, which leads to the battle on Japanese terms that the Japanese wanted.
Case III: Japanese victory: Not out of the question, the initial American attacks did get savaged. The point of divergence could be to take Spruance out of the picture (as a submariner he's an unlikely candidate for carrier command) and replace him with someone of less competence. Results are as for Cases I and II, but more so.
An easy German occupation of Stalingrad, for whatever reason, might have some impact but probably not a huge one. Pushing through to cut off and (perhaps eventually) occupy the Caspian oil sources could be very important. I'm unsure how important Stalingrad was.
Mentioned mostly so I can dismiss it: the Germans are too far gone by this stage for any single battle to save them.
Normandy was a spectacularly brilliant deception operation and a logistical triumph. Even so, there was one beach, Omaha, where it all went horrible. What if everything that historically went right had gone wrong, and there'd been five beaches like Omaha? What if the invasion had turned into a bloodbath, pinned against the channel and eventually evacuated in disgrace, or even overrun? It would be the end of any significant allied effort for 1944. By the time they were ready to try again the Russians would be knocking on the door of Berlin.
The Me-262 was a primitive jet fighter. Its production and development were held up by Hitler's odd obsession with converting it into a strike aircraft.
Case I: Germans develop jets earlier: It'll hurt, but it can't really turn the war around. The US, Britain and USSR will presumably accelerate their own jet programs in response.
Case II: Germans fail to develop jets: This may retard jet aircraft.
Case III: Allies develop jets sooner: P-80s, MiG-somethings and/or Gloucester Meteors battle Me-262s and Arabo blitzbombers. All good fun, and jet technology may be accelerated, but probably not a huge impact on history.
The Germans had most of what they needed to produce a nuclear fission bomb. The big problem was resources generally, it's hard to see Germany funnelling the vast sums into their program the Americans could into theirs, unless Hitler gets obsessed with the idea. They had Werner Heisenberg to run it, but they'd also lost a lot of brilliant scientists like Albert Einstein and Enrico Fermi, and made no visible effort to recruit Nils Bohr. Their concept was completely wrong (they thought they'd need to build a reactor and make it go supercritical, which rules out bombs small enough to be transported in aircraft) but that can be taken away by POD. If the Germans get the K-bomb early enough (from kern, the German word for nuclear) they'll probably drop the first one on London or Moscow. A later target might be Antwerp, or some critical centre of communications on the Eastern front.
Nuclear weapons were invented for the purpose of attacking Germany. Let Germany hold on six months more and they may be. The postwar consequences are probably the most interesting: Germans may have stronger negative feelings about nuclear power, nuclear weapons and Americans.
The US didn't realise it, but Japan was ready to surrender when the Hiroshima bomb was dropped. A translation error was partially responsible for the confusion: nobody should discuss sensitive subjects with foreigners in a language as deliberately obscure as Japanese. The final straw had been the USSR's entry into the war, since the Japanese had been hoping the USSR would mediate. If America realised Japan was about to surrender, or if Japan surrendered sooner, maybe just a few weeks sooner, there might never have been a nuclear weapon used in anger. The post-war issues could bear a lot of scrutiny: America thinks the bomb is a secret, but it isn't. The USSR knows about the bomb, but maybe Stalin will be sceptical of his scientists' aapparently hyperbolic descriptions. Both sides will capture German scientists from Heisenberg's project, who will think the project very difficult. But maybe not say so, since they're all unemployed and in danger of becoming slave labourers if they can't prove themselves useful. What if Russia builds a nuclear arsenal in secret? How long before scientists and science fiction writers start wondering aloud why nobody's been working on this? Or before the news leaks: scientists are very bad at keeping secrets, at least amongst themselves.
At the end of world war two the allied and Soviet armies met across a vanquished Germany. What if the meeting had been violent? The Russians have a huge army, but not much manpower left in reserve. The western allies have the arsenal of democracy, lots of airpower and the sympathies of any German military units that have survived (e.g. the Norway garrison, von Kesselring's army of Italy and that division that got stuck on a channel island) or can be formed (e.g. from POWs). Best of all there are nuclear weapons in the pipeline. The Russians must win fast, or they won't win at all: of course, the best they can possibly hope to do is overrun Germany, France and just maybe Italy, so there'll always be a base for the allies to come back or at least strike back. The French, Yugoslav and Italian communist partisans will presumably fight as allies of the USSR. The Japanese have a glimmer of hope that they never deserved: if they get an offer of peace from the allies short of total humiliation they will accept; if they don't they will fight without real hope, notionally alongside the Russians.
Case I: The western allies start it: I don't see how to arrange this, it probably requires a conspiracy between, at a minimum, deranged analogues of Roosevelt, Churchill and lots of other people. Let us never speak of it again. OK, maybe a deranged analogue of Patton starts it and it gets out of hand. But sooner or later someone will try to pull the plug, if Stalin will agree. Not a really plausible POD.
Case II: The USSR starts it: Stalin's paranoia points outward for a while, instead of inward. Maybe the POD is a clever Red Army general who deliberately redirects Stalin's attention as the only way to prevent another purge. A lot of people in Russia will be unhappy and they'll take any good opportunity to depose Stalin if they think they can make terms. Or maybe Stalin realises what nuclear weapons can do and thinks he has to strike now, which is a really dumb way to think but who knows the mind of a mad dictator.
Case III: Both sides think the other started it: Probably the most likely POD. This makes for a bitter conflict, both sides are crying infamy and are in no mood to accept anything less than unconditional surrender. The blue glow of Cerenkov radiation replaces street lights in many Russian cities.
Why not tell me about it? Or, better, write it up yourself.
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