It is definitely a change making a simple map rather than anything detailed from time to time.
A common AH topic is the Axis winning WW2. One can often see maps showing a complete Axis victory or a German (+ Italian) victory with Japan being defeated. I decided to go the other way around.
PoD: Japan declares war on USSR some time after Operation Barbarossa starts. In addition, Japan does everything in their power to keep USA out of the war. Finally, USA joins the war on the Allied side, but only against Germany; this is not enough to prevent the fall of USSR, but German and Italian fascist/nazi regimes fall several years later. The Second World War finally ends in 1947, when both the Japanese and the Allies realise they cannot hope to gain anything from continuing the effort. A Cold War develops with Aberdeen Global Defence Union (named after the city where the creation conference took place), i.e. former Allies, and Global Alliance of National Governments, composed of Japan, Persia, Thailand, Saudi Arabia, Ethiopia and Argentina. Add a much different decolonisation and twenty more years, and you get this:
Alternate scenario. Trotsky wins over Stalin. More agressive USSR, more dedicated to spreading the world revolution. Tries to kindle revolts in Iran, India, Greece, etc. etc. USSR even less popular than OTL.
Don't trust Chiang, decide to throw heavy support to more radical wing Kuomintang. Mao and Co. does much better, and after Communists are routed out of the south, grow in the N. and west much faster than OTL. Chiang assassinated by Communist agents, south falls back into warlordism, and when the Japanese invade it's with the applause of much of the world, who see them as preventing a Soviet takeover of China. USSR-Japanese war 1937-1938, Japanese lose much of their territory, forced back to some coastal enclaves and Korea. Rather than pursue fight to the finish, Soviets make an armistice, worried about Hitler.
No Nazi-Soviet pact. German embassador gets packed back to Germany in the cheap railway car for suggesting such a thing. So, Hitler goes west. French armies still led by elderly twits, Germans still win, although slower and bloodier than OTL. (No chance to practice on Poland first). Trotsky, seeing he's next, decides to strike first, invades through Poland.
Roosevelt has a much tougher row to hoe in this TL. Although people are suspicious of Japan, they are currently keeping Red north China out of the south, and Trotsky hit first. He manages to get Lend-Lease for the UK, but nobody is ready to help the Red Napoleon overrun Europe.
Trotsky's army is better generalled than OTL, and is on the offensive. This is counterbalanced by no lend lease, a Germany without any side distractions in Italy or North Africa, an immediate and earlier move to a fully mobilized war economy, the need for the Soviets to keep more troops in the east to deter a Japan with no American distractions, and a smaller industrial base (Trotsky took longer to consolidate his position than Stalin, and simply hasn't had the time to work as many people to death building a giant war machine- indeed, from a Stalinist position, he's put a shocking amount of limited resources in giving plumbing and electricity to
peasants.)
In the end, Germany wins, but it takes until 1945 to win the bloody war of attrition. Still, by April of that year German forces have reached the Volga, Trotsky has been toppled in a military coup, and a General has made peace to preserve what is left of the USSR (east of Omsk, a Trotskite loyalist government springs up and is soon at war with the Kazan government). Just in time, for the US looks like it's gearing up for an invasion, Italy is mostly lost, and the US airforce dominates the skies.
Roosevelt was finally able to scrape together the votes for a declaration of war in early '43, after a long and depressing series of German victories, atrocities stories leaking out of the continent, pictures of starving French babies, and brutal sinkings of civilian ships. But with a start to full mobilization some 16 months later than OTL, it wasn't until the summer of '45 that an invasion of France was possible, and then against an enemy with many more troops to spare.
The Japanese, meanwhile, had not been idle. Leaving alone directly Soviet-occupied areas such as Manchuria and Mongolia, they had launched an invasion of Red China, nominally as allies of a bunch of anti-Communist southern warlords and "republican" governments, correctly calculating that the Soviets would not retaliate while tied down against the Germans. By '44 they controlled most of N. China (although some territory would be doled out to their more servile "allies"), and paused for events.
The US gathered an even larger invasion force than OTL, and managed to batter their way onshore. But the German had More troops than OTL in Germany, more planes, and more jets - Allied bombers had been unable to entirely stop Romanian oil production (the line from Baku kept getting dynamited by partisans). "Breaking out" of the beacheads took months and a massive buildup, and Allied forces did not reach the Rhine until the next spring, after a horribly bloody battering. German forces were still holding on stubbornly in bomb-flattened Berlin (the eastern borders of the empire were still deep into Russia) in December 1946, when they, much of their city, and the Fuhrer went up in atomic smoke.
The Second Russian Civil War started in May, after US forces breached the Rhine, when Trotky's usurper was in turn assasinated as a German puppet. Trotskyites, Leninist ultra-hardliners, moderates calling for left-coalition rule, even a few monarchists and democrats, struggled for control, while certain elements of the army launched attacks on the now much-thinned German occupying forces. Meanwhile, the Siberian People's Republic launched it's armies west, and was promptly attacked by the Japanese. (When the US grumbled this made them essentially German co-belligerents, the Japanese ambasador tartly replied the US hadn't had the experience of living next door to Trotsky's Russia, an experience that they had no desire to repeat).
The last German holdouts were wiped out in '47, and the US found itself occupying Europe from Germany to the Ukraine. The Japanese, meanwhile, had driven the Trotskites west of lake Baikal, and were consolidating their control of the northern third of China, where a harsh communist rule and a purge of "capitalist" elements made a sizeable part of the better-off inhabitants somewhat grateful for (mostly indirect) Japanese rule. In the south, Japan generously supported rulers willing to put their welfare and the benefits of being a big frog in a small pond ahead of Chinese unity. (the lack of a "burn all, kill all, etc." policy helped, too.)
In Russsia, the Second Civil war would not end until 1950.
Bruce