That's right, folks! More Nazis! This is a 1940s dieselpunk world, so of course the Nazis rule a good part of the globe.
It is the year 2040, and the Second World War rages on. Not as a proper conflict between armies, of course. That ended decades ago. The war continues on as a guerrilla conflict on the Nazi-Soviet Front, as the waves of bombers and ballistic missile salvos between the Reich and Airstrip One, and the very occasional conventional wars between the Allies and Axis in the Middle East. There are two new orders, each vying for total supremacy, each unwilling to accept a world where the other exists. But the stalemate has gone on for so long that it has become impossible to break.
The United Nations is led by the United States of America, the Empire of Liberty, the Arsenal of Democracy, heir to the Anglo-French alliance that first battled against Germany. The United States is led by the New Deal coalition, a very shaky alliance that has somehow survived for over a century. This survival is attributed to the establishment of various "regions" where the New Dealer factions have total dominance; Southern segregationists own the South, ethnic minorities have enclaves around the country, trade unions own the cities, and liberals own the North. The Republican Party exists, but it has not been a legitimate opposition since the 1980s. The Republicans instead are a group of boogeymen, populated entirely by double agents from the New Dealer faction and preaching what a carbon copy of the Nazi program applied to America. The New Deal coalition has total control of the country, and indeed their party machinery has totally replaced the civil government of the United States. American civil offices are merely ceremonial statuses awarded to retiring party loyalists or the losers of power struggles being exiled to become governor of Montana or somesuch. Americanization is winding down in the Pacific territories, as it has been deemed completed. Too bad about the Japanese, though.
Surrounding America's orbit are the other Unions. These unions were formed at gunpoint by the Americans as the front solidified and fascism and nationalism had to be rooted out. Only unity through a democratic program could effectively fight fascism, and so the Americans imposed it on the world, whether they liked it or not. The various Unions have differing flavors that keep them unique. The United States of South America is less a union and more an organization of military juntas loyal to Washington, yet with their autocratic practices, frequent discrimination against native cultures, and awesome uniforms they do bear more than a passing resemblance to Germany. The Soviet Union remains nominally under Stalinism, though Stalin himself passed long ago, and communism has given way to the deeply religious, deeply nationalistic Russian "unity politics." The Federal Republic of India is a veritable Frankenstein's monster of religions and ethnicities that its "Unity" government is trying to erase and replace with what is essentially American culture as seen a century ago. The Union of Oceania has successfully Americanized, and many schoolchildren think that the British had nothing to do with Oceanian history. And the United Republics of China continue to do their own thing, Sinicizing their portion of the world and brutally putting down any opposition as the Americans ignore them.
Then there is the Greater German Reich. The autocracy of Hitlerism hasn't survived the 20th century, with infighting nearly bringing down the Reich in the 1950s and 1990s. The Third Reich has begun to resemble the First Reich in many respects, with governors, gauleiters, oberstgruppenführers and generals each having their own little empires to govern. These authorities tend to overlap and twist on themselves, creating a great deal of confusion and political intrigue that has left many high-ranking men dead from lead poisoning. However, the Reich is united in its opposition to the United Nations and its continued dominance of the European continent. The "undesirables" have been exterminated, at least in Europe, and now Germany moves to Germanize the remaining population of Europe. This program has been met with great success, and now Welthauptstadt Germania plans on bringing more of its European Confederation into the Reich proper. Lebensraum awaits!
Germany's allies only remain so due to terror, and as they become liabilities it is uncertain if the Germans would tolerate them for long. The Italians, still under Fascist autocracy, has gradually adopted their own version of Roman-Italian nationalism that has rejected Catholicism in favor of the old Greco-Roman gods. The imposition of this system is causing major problems in Italy, giving Germania concern. The Atlantropa project is also failing to meet Italy's expectations; instead of giving Italy more farmland, the recovered lands are quickly turning into desert. The various members of the European Confederation and their fascist parties are skeptical about Germany's intentions to protect them, as it becomes clearer that the Germans will not get the lebensraum in the East that they desire. As for the South Africans, they only joined Germany because it was advantageous at the time, and the Germans seemed more friendly to their white supremacist ideology. But their membership in the Axis grows less palatable every day.
The wonders of diesel technology keep the world turning. Great zeppelins move troops from the United States to Airstrip One. Rocket planes zip across the world, delivering passengers or bombs to their intended targets at record speeds. Tesla technology has allowed armies around the world to shoot down rockets and bombers by the thousands, but the massive waves each faction sends ensure that at least some get through to do some damage. Diesel-powered automatons gradually replace soldiers and factory workers, leading to mass unemployment that may have very bad consequences later. New materials technology have allowed buildings to climb higher, with the great megalopolises of BosWash and Germania reaching past the clouds. Experiments with atomic power led to disaster; any atomic reaction of note would have to be so large that it would burn the atmosphere, as the Martian example tells all. It's a shame, really; perhaps the bomb could have put an end to the war.