Infodump!
The Great War breaks out in 1937 over the assassination of the Serbian Minister of State by pro-Bulgarian rebels in Macedonia, and lasted until 1944. It was a nightmare really. With not proper military experience since the Franco-Prussian war no one had any idea what to do with their shiny new bomber wings and armoured cars. The Soviets were delayed from entering the war with the sudden death of Premier Trotsky and about a year of instability as hardliners and liberals did battle. This left the French and British in dire straights trying to fight the Germans. The lack of understanding of how to run a motorised offensive was the main saving grace of the Entente. The Japanese then surprised the world by siding with the Germans in exchange for the undefensible German Pacific.
The Central Powers and Japan were skipping merrily through the daisies until two incidents happened. The liberals took control of the USSR and decided to demand "their" Baltic back from the Germans, and the Germans felt the USSR was on the verge of collapse and had kept about a 3rd of their army in the East anyway and hoped to gain some swift victories to secure the Ukrainian breadbasket. The initial offensive was successful, but the eastern front quickly became as indescicive as the west. Then a German U-boat sank an American cruise ship (that was smuggling weapons to the Entente) which happened to be carrying famous American Actor Guy Caballero. The public outrage was swift and the Americans stumbled into the war. Japan began trying to probe negotiate a way out of the conflict realising that they couldn't counter the American industrial might, however Britain, France, and China refused the Japanese terms as they knew just as well what American intervention meant.
The Americans concentrated on Europe first, and poured vast amounts of manpower and steel into the war, while the Soviets had manpower but were a bit lacking in industry (American aide mostly made up for this though). In the east the Americans only really committed Navally for most of the war, until 1943 when the Bulgarians defected to the Entente. This shifted the balance in the East allowing the Americans to send more troops to the east. The offensive ground down at two points though. The Marshall Islands assaul plowed through the Japanese Garrisons until it reached the final island (Lagos Island) where a full division of marines was lost reportedly to an assault by dinosaurs (something that would have been dismissed as nonsense if not for the Kong affair). The second, and more spectacular point, was the Japanese releasing their flying battleship known as the Gotengo. This ship smashed through the American fleet for several weeks, breaking their momentum, but was eventually brought down at the battle of Minto Reef, where 8 carriers and 6 battleships, along with a variety of other smaller craft, brought the great ship down. The American's offensive was broken, but the Gotengo had been Japan's last great effort and her navy was even worse for wear (plus the American industry was set to replace material losses within a year at the worst). When the Soviets launched an invasion into Japanese occupied China and Rolisica invaded Sakhalin the Japanese knew the game was up, and the Japanese armistice on Oct 10th 1944 was followed by a German one a month later on Nov 11th.
The Entente won the war, but bungled the peace. Germany was left bitter but not properly defanged, and the same was true in Japan but to a lesser degree. The Americans had marvelled at the Gotengo and in exchange for it's ruined hull and design information Japan found itself only lightly punished. Germany however was forced to pay vast sums of money and hand over her allied states.
Fast forward to 1954. Germany has fallen under the control of the Authoritarian Volks Party, which has declared a Third Era of German Ascendence. Britain and France grow strained by their colonial Empires. The Soviets have grown to detest pro-Western puppet states and hope to spread the revolution, China being central to this. The USA has become the world's first nuclear state, but the USSR, Japan, UK, France, and Rolisica all seek to copy this success (the Rolisicans are particularly desparate as Soviet spides pervade their ever more authoritarian state).
And yet the world is about to be shaken not by the acts of man, but of beast as the Age of Kaiju begins!