With any PoD after 1900, and preferably after the assassination of Archduke Franz-Ferdinand, have Germany and the Central Powers win World War I. If Germany won, would it get its Mittleafrika colonies that it aspired to(it could take the Congo from Belgium). What would be the situation in Europe TTL? How would France handle a second humiliation by Germany? What would happen to Austria-Hungary and the Ottomans? What would be the longer term effects? What if?
Hmm, for mine I set 1890 as the divergence period and altered a few points during and after the Boer war to make the British military modernisation less efficient (terminating Lee Enfield and .303 production before the new .280 round and rifle are ready, no Haldane reforms et cetera) and killed off Churchill in 1911 (his idiot grandstanding got him a bullet[1]) so the British forces were significantly but not enormously (say 5-10%) less efficient (less emphasis on aircraft, dithering on the use of oil fuelled engines [2] et cetera). The Germans won in 1915, though it was more of a negotiated peace than total victory.
The consequences were: [not exactly plausible, I had a particular endpoint in mind]
1. Germany experienced a lurch towards the Social Democrats and democracy in general, while maintaining significant control on it's not-really-an-empire in eastern Europe.
2. France was pissed, went revanchist but later softened and relations with Germany improved, especially after the spread of authoritarianism/fascism in the mid thirties.
3. Russia fell apart, messily, but managed a weak central government. After the Big Slump it went pan-Slavic/religious/anti-Semitic/imperialist nuts and tried to conquer the world.
4.This caused the Eastern (or Autumn) War [3]. This got nasty [4]. Parts of eastern Europe are still fenced off.
5. The Austro-Hungarians managed a controlled, slow motion, collapse under Franz-Ferdinand into a Danubian Federation. Some bits merged into Germany after the Eastern War.
6. The Ottomans held together until the 1960s when a series of smallish civil wars triggered EuroFed intervention.
7. No Spanish Flu. Instead A(H1N1) arrived in the mid thirties during the Big Slump as the "Okie 'flu".
8. The United States isn't. It came apart under a morass of economic and political problems in the 1930s too, though without 'proper' civil war. The situation isn't particularly bad (at least once the New Confederacy was toppled[5]). By 1970 there's a Canadian/Californian/New England dominated North American Confederation that's rather like the OTL EEC but with distinct federal ambitions.
9. As of 1970 the world's favourite rogue state is the British Republic, it's one mighty empire almost gone there's growing concern about what will happen when it finally collapses.
10. The European Federation is a social democratic super-state and
the global superpower. It's rather complacent expecting the world to eventually embrace the One True Way of social democracy. It has a few shocks coming.
11. Other significant players are the Indian Federation (a nice place to visit unless they think you're English), Imperial Iran, the Japanese Empire (probably going to allow women to vote soon), China is, well China is a mess. South America is (without meddling from the north) becoming more unified and developed; currently the continent is dominated by a EuroFed aligned Brazil and a more neutral Argentine-Chilean block.
Nuclear weapons are common, and occasionally used. They're viewed as useful tactical problem solvers rather than end-of-the-world nightmares. Threatening mass city busting is passé, suited only to uncivilised and desperate (i.e. Britain).
12. Technology is rather more advanced. Personal computers and a rudimentary public internet exist, Mars has been visited and there are a couple of lunar bases and lots of stuff in orbit (including an interesting variety of weapons platforms).
Oh and there are aliens, invading pretty regularly and leaving bits of technology behind. And time travellers. And hibernating reptile people.
The 'one-percent' are quite aware of this.
[1] Well
actually it was a time traveller but technically that wasn't a change to history.
[2] This would have significant long term consequences as Britain wouldn't become involved in the Middle East to the same degree (Anglo-Persian Oil Company) and would later be reliant on oil supplies from other sources, which would lead to the bloody maintenance of rule over British Nigeria.
[3] A term coined in the 1960s by a pair of historians who wrote the authoritative history of modern Europe. The Spring Wars were the period from 1870 onwards that created "modern" Europe, the Summer war was what we'd call WW1, the Autumn War was Civilised Europe v The Slavic Hordes (there was a tinge of bias). The Winter War is what we'd call the Cold War but with more players.
[4] Not quite to
The Shape of Things to Come nasty but chemical weapons were used enthusiastically and the chemists came up with some
interesting agents (chlorine trifluoride was used a little, for example) including second and third generation nerve gases. There was limited used of biological weapons (including anthrax) and more than a dozen German developed superbombs went off.
[5] People in this world have
Views on the subject of state organised genocide, Russia was a one-off and no-one's going to tolerate a repeat, even of the brown-skinned. EuroFed and the League of Nations can move quite fast when public opinion is mobilised.
Also the Confederate nuclear weapons programme wasn't going to be tolerated.