*No Pearl Harbor. Japan works very hard not to antagonize the US to any degree beyond what is absolutely necessary and the Japanese Navy is told to avoid American targets whenever possible.
*Japan still takes control of French Indochina as OTL and heavily plays the "Asia for Asians" card. They also approach the British and negotiate a deal: In exchange for resources and security in the East they get a "protectorate" over the Dutch East Indies, a free hand in China, and preferential trading rights in Hong Kong. In return Tokyo renounces the Tri-Partiate Pact and joins the Allies
*US enters war in August 1942 and it is not nearly as popular as OTL on hte homefront but a Germany with the possibility of dominating Europe can not be denied. They do not declare war on a fellow Ally and make it clear further adventures in Asia will not be tolerated. Much of coastal China ends up in Japanese hands following the Treaty of Mumbai in 1944, the rest becomes a series of rump warlord republics that answer to Tokyo.
*After the war decolonial influence leans many to follow Japan's lead as satellite states. Japan gets her Co-Prosperity Sphere without nearly the loss of life or resentment that outright conquest would bring. At the same time she keeps most of modern eastern China, Korea, Taiwan, and Indochina along with many smaler Pacific Islands.
*By 1990 the Co-Prosperity Sphere is one of the leading economic powerhouses and with the fall of the USSR talent finds its way to the major research centers at Tokyo, Osaka, Seoul, Taipei, and Shanghai. A common currency is brought into being and is more stable than the Euro though less than the dollar.
*By 2010 the economy sees languish in Bangladesh and Indonesia but bailouts from Tokyo prove fruitful, the E.A.C.P.S. now includes Afghanistan, Persia, India, and Pakistan with control of all of Asia outside of Russia and the Middle East. Japan herself, now called the Dragon Empire, rules much of the eastern third of China along with the aforementioned areas