So, I'm working on a little alternative history for a diesel punk setting. Part of the inspiration was how I wanted to use DF Les Grognards, and my being slightly bored with all the Weird War 2 stuff. I mean, do we really need more nazi zombies? Don't answer that.
Anyway, it's the 1920s the Great War hasn't ended, and is being fought in nearly every corner of the earth with weapons that may rival what we have today. It's an age of great empires and quickly shifting alliances.
Much of Europe's history has roughly followed a similar trajectory of events as we know them, though the Tsar is still in power in Russia. However a key difference is Charles Babbage unveiled a fully functional analytical engine in the 1850s. No one really knew what to make of the device, until inevitably an enterprising artillery officer used one of Babbage's devices to calculate gunnery solutions, kicking off a revolution in computerised warfare.
In 1905 Percy Ludgate a young Irishman introduced the world to the first analogue electric computer, building on Babbage's work in a novel way. Leading to a second electronic computer revolution. by the 1920s The Ludgate and Babbage companies are the dominant analytical computer manufacturers in the world.
Some of the most divergent events are in the Americas, with the Mexican empire being established in 1821, and not being overthrown after 2/3 years. The Empire of Brazil dominates South America and both the Brazilian and Mexican Monarchies are still largely in power at the outbreak of the Great War. The Brazilian empire is a major player on the geopolitical stage, and supported the Confederacy during the ACW, to ensure a weakened northern neighbours in the Western Hemisphere.
North's America is geographically dominated by Mexico and British Canada. With the USA and CSA dividing up the eastern seaboard. Columbia District(Oregon, Washington and British Columbia) was sold to the Empire of Japan in 1918 by the British to fund war efforts against their enemies. Alaska is still Russian America. Slavery is still legal in the CSA.
In Europe, Ireland never launched it's war for independence, as the Great War is still going on. Switzerland isn't neutral, having sided with Germany and Austro-Hungarian empires. Many countries that were on the map a few years ago only exist in memories. In some ways you might say Germany has won, but the Austro-Hungarian empire has imploded into civil war. Much of the western front is still an active warzone, with new innovations rarely making much of a long term difference.
The modern battlefield is dominated by terrifying new war machines, automatic repeating guns and the smell of diesel and poison gas.