US doesnt join WW1 due to more germanophile sentiment. Germany is defeated in mid 1919. All ex-german pacific possessions that went to the US in OTL go to Japan, so in addition to all they got in OTL they gain Guam, Wake.
After this, things develop as they did in OTL for awhile. Come WW2, there is much greater isolationist sentiment in the US than in OTL. This cause Roosevelt to fail re-election in 1940 as many americans doubt his commitment to true neutrality. America then stops pressuring Japan about the situation in East Asia.
The war continues in Europe. In the pacific, the non-embargoed japanese continue their gains in China, gain Indochina completely from Vichy, and push for bases in Thailand. Tensions increase with the British who keep supplying China but to avoid angering the US, the japanese, who are not as hard-pressed as in OTL for ressources, limit their ambitions. By 1944, the japanese successfully push into central China, finding truly little organised resistance along the way. Formal negociations are opened, with the Manchukuko puppet poised to take over all the country.
In August, 1945, with the soviets at the gates of Warsaw and the British gaining ground in Italy and the Balkans, a coup occurs in Germany. The military leadership pulls out of France, the Low countries, Italy and most of the Balkans. V2s stop raining on London. There is no unconditional surrender doctrine and Churchill is hard-pressed to make peace. There are even greater worries than in OTL that the Soviets wont stop till they are in Paris, and much less means to stop them this time around. After the separate peace in the west, Germany forces the SU into accepting the return to the 1940 borders.
The world rebuilds, and America is increasingly the preeminent power, the only one from having not pertaken in war. In 1955, nuclear weaponary is first tested in the US. Japan retains her Empire, and Germany very generous borders.
Japanese rule in Asia softens over time, but to this day, most of the pacific islands remain in her possession. Her staunch refusal to embrace western values persists, but the japanese people thrive nontheless.
In Europe, the long military regime followed by Germany's return to the imperial age leaves Europe split to this day, with no notion of unification anywhere in sight.