alternatehistory.com

The World War was the final conflict of the European Crisis. Also called the Last Colonial War, this conflict was the deadliest in human history, and raged on every continent.
It found its roots after a border disagreement between France and Britain in Nigeria turned violent, with casualties on both sides. Tensions between the two colonial powers had by then reached a critical point due to their different interests during the European Crisis, and rivalry since the Napoleonic Wars. War soon followed, and just like that, the Accords and the Allies found themselves at war.
For Japan, it wouldn't change much. The Japanese had been at war with the Republic of China since 1938, and made good progress. With Russian intervention, Japan soon controlled half of the country, with the PRC making its own advances in the south of the country against the ROC, who had also been in the middle of a civil war. However, the alliance to the Netherlands would shelve plans to invade, but not their plans to invade the Philippines, which they did in mid-1941. With that, the US intervened, but did not declare war on Britain or Russia.
That would have to wait for early 1942, where the U.S had finally mobilized its full force on the Canadian border. The North American front was a formality for the U.S, who ran over Canada in six months, and contributed to the Quebecan Uprising. The quick invasion also isolated the U.K even more, who was losing steam after their European Campaign ran out of steam after the failed Siege of Verdun and the Ruhr Offensive. With the Russians also failing to take Krakow and link up with the British in Berlin, and with the fall of Piedmont to the Allies, the U.K had to be on the backfoot from then on.
Even more worrying, although the Royal Navy had protected the British Isles (except for the Channel Islands), they had been badly beaten in the Mediterranean, where French, Provencal and German troops had managed to push all the way to the Suez Canal by 1943, and isolated Malta and Gibraltar. Despite this, the two strongholds would not fall until 1945, and Britain would be permitted to keep them along with the city of Suez, which all held for two years.
In subsaharan Africa however, the situation was much more chaotic. Apart from South Africa, Djibouti and everything west of the Huntziger Line, everything else fell into chaos, with most troops being pulled back for more important duties. Thanks to harsh colonization, order quickly broke down and several countries declared independence and soon fell into civil war (one notable example being Nigeria, for which the war was fought in the first place).
In the Middle East and South-East Asia, the U.S intervention made Persia and Siam's position even clearer. France had already promised Siam territories in Cambodia in exchange for their intervention in the War, which they entered in late 1942 with the Allies. Persia would follow suit on the side of the Allies in 1943, pincering the Raj. The Indian Coalition, made of Hyderabad, Mysore, Tamil, Pakistan and Bengal would also rise up, although Pakistan would be crushed and later divided between Persia, Afghanistan and India. The Raj never fell, but did have to capitulate with the U.K.
Indeed, in Europe the situation had become dire, with the Accords being forced out of mainland Europe by mid-1943, with the fall of both Amsterdam and Copenhagen, as well as the failed Normandy Landings. In the East, Russia had been pushed back to Smolensk and Kiev, as Bulgaria forced back Greek and Romanian offensives, reclaiming Dobrudja by 1944. The U.S intervention also helped speed up the invasion of Britain, as although the Royal Navy had been beaten, it still had superiority over the British Isles, which the U.S Navy helped remove at the Battle of Ushant. Operation Constellation then began, marking the beginning of a two-year campaign in Britain. Britain didn't capitulate first though, as Moscow fell in June 1945, 5 months before the fall of Liverpool.
The last to fall was Tokyo. After a gruelling war in the Pacific, where Australia had managed to render easier by defecting to the Allies in 1942. Despite the defection, there were battles on a great number of islands, with Batavia falling only two months before Tokyo, while both Hong Kong and Singapore never fell despite Siamese intervention. Manila was reclaimed in late 1944, while the Japanese lost Okinawa and Formosa by 1945. Not wanting to put American lives at risk, the U.S put their nuclear plan into action, wiping Hiroshima and Kure off of the map and forcing the Japanese to surrender.
Two seperate treaties were needed to end the war, one in Versailles for the European powers, and one in Darwin for the Pacific and Asian fronts. Africa on the other hand never got an official treaty due to the ongoing conflicts, the only issue needing to be settled being that of Egypt. The War directly led to the collapse of both the Japanese and British Empires, although both were allowed to keep their gains in China (although Japan had to abandon Korea and transfer it to U.S hands), as the PRC had nearly overtaken the Republic by that point, triggering the First Chinese Crisis, which resulted in Chinese Isolation and the need of International powers to keep positions on Chinese soil in case the PRC started to become a little too confident.