The Entente was much more successful in WW1, dividing Austria and releasing Poland as per OTL. Then something went seriously wrong and Greece and Italy united to become the New Roman Empire. Meanwhile in Russia gradual reforms were introduced and the Bolsheviks never gained power. In its fragile state Russia could not stop their western-most provinces from seceding however, but compensated for it in a war 20 years later in which they aided the Neoromans in defeating Turkey and invading Iran just for kicks. Thrace saw a "population transfer" that makes OTL look downright friendly and civilised. At this time the British were busy fighting France, who had guaranteed Ireland independence just as the Brits were about to invade the young republic. After a bloody war the two great powers agreed to status quo ante bellum, and over the next say ten years or so Ireland grew so close and dependent on France as to be considered a satellite.
America never intervened in WW1. Instead they saw the depression crippling their nation and angry workers rising up. The American revolutionaries found friends in Mexico and after the second civil war was over and the commies had the White House repainted red, they invaded Mexico to aid their proletarian comrades to the south. After crushing the Mexican bourgeoisie scum Mexico joined the United Socialist States of America, greatly expanding the extent of the Union. Who then went on to spend the 30s and 40s dominating Central America and supporting communists world-wide.
Russia, fearful of communism after their own failed revolution, intervened and occupied Alaska during the second civil war. Then they made it their puppet. Japan also took the opportunity to invade the Philippines, then presumably tried to take China but failed and decided that the whole imperialism thing wasn't for them after all, what with most of Europe keeping an eye on them after their failed attempt at great power-hood.
Decolonialisation has been avoided for now, and in the late 40s the British Empire reformed into the Imperial Federation, giving a measure of autonomy to their former colonies, now equals in statehood.
How's that?