The Great War ultimately ended in a victory for the Entente powers. The German army, despite its advances into Poland, was ground down by superior Russian numbers and production capacity. Ultimately the Russians broke the back of Austria-Hungary in 1918, resulting in Germany's surrender as Communist and Republican revolutionaries tore the country apart. Russia dominated eastern Europe, a domination that has yet to be broken despite the challenges of the Second Great War.
Russia and Britain's Republican ally, on the other hand, fared significantly worse. France, true to its revolutionary tradition, suffered a Communist revolution, shocking the world. In hindsight, the reasons for these dynamics are clear. France had a proletariat that was far more class conscious, and had an established revolutionary tradition in Paris; meanwhile, the Russian people were fully behind the Tsar in what they saw as the second Napoleonic invasion and the conditions in Russia were completely wrong for Marxist revolution. Your challenge, then, is to switch the fate of France and Russia; have France survive the war intact and a great power, while have Russia collapse to Communist revolution.