I think the Point of Divergence would be Roosevelt getting another term, knowing him, he would've looked through heaven and hell for a reason to fight the Germans. Roosevelt would send supplies to help the war machines of the UK and France. The German U-Boats were told to attack any Allied ships, but a ship carrying troops, including Archibald Roosevelt (Teddy's son) was sunk. Teddy went to Congress and the rest of the US with the fire of a thousand suns in his soul. He then read the famous "Remembrance and rage" speech, where the nation remembered all the loses, and swayed the heart of the nation, the US would go to war three days later.
Allied trenches were suddenly filled with American troops, and eventually German trenches were filled with corpses. Many important things happened during the "American Crusade" as it began to be called, African Americans were allowed to join the Military, Trench Buster cannons were built, and German POW created an anti-Democratic Manifesto that seeped into Europe. The latter event would be more important, because this German, Heinrich Himmler, would return to Berlin (with the help of Austrians) and toppled the Berlin government, the day would be called "The Fight of the Fascist", knocking them out of the war.
Austria-Hungary was invaded by Americans, Brits, and French troops. The Ottoman Empire decided not to risk it and switched sides and attacked from the south. Budapest was invaded, and Vienna surrendered. Germany became a nation wanting the destruction of Democracy, the Muslims, and Monarchism. Austria and Hungary were separated and became puppet states of the Allies. The Ottomans switching sides ended well for them, the keep all their lands and claim most of the middle east. Russia became Communist under the leadership of Leon Trotsky. Trotsky would gain other Communist countries to join in his "Eternal Revolution", which is invade Europe.
Fascist Germany (reluctantly) joins the Allies to stop the Communist threat. After the Allies dissolved the USSR, The US Ended the war finally in Communist China when with (I know it sounds a little ASB) a bomb capable of destroying the city of Beijing. Fascism would spread to the world with the fall of Communism. A non-violent war, the silent war, would rise between Capitalism and Fascism, eventually ending with the economically less gifted fascism, with a splintered Germany. The only remaining Fascist states would be South Korea, Japan, Argentina and Chile.
That is how I think it would be at least, sure the "Super bomb" sounds made up, but it could be built, there are real theories about it.
