I'll go with a White Dawn 1945.
1914 POD: Franz Ferdinand not assassinated, WW1 averted
1917: Imperial Russia completes modernization of Russian military
1918-1920: WW1 erupts, France and Russia partition Germany, Duma subsumes power over Czar, reducing him to a figurehead
1924: Russia annexes collapsing Austria-Hungary, leading to souring relations with West
1932-38: Russia declares war on Imperial Japan as a way of distracting their populace from the economic perils of the Great Depression, Russia annexes Manchuria and Korea--finds out that many of its WW1 weaponry and strategy is out of date and begins another massive modernization, particularly of their navy.
1938: Imperial Russia has world's largest GDP
1941: France, Britain, US, and Japan form a defense pact against Imperial Russia
1944: Russia has world's largest naval fleet, about 70% of the size of the Royal Navy and US Navies combined
1945: Russian intelligence detects coordination among the Entente to attack Russian holdings across the Rhine. To pre-empt any Allies attacks, Imperial Russia draws up a plan to attack first globally. On th first day of war Imperial's Russia's navy destroys the Japanese fleet in port. A large Russian landing force lands in Alaska, easily overwhelming the Americans. Months later the US fleet meets the Russian fleet in battle over Midway Island. US Pacific Fleet s decisively defeated, the Russian navy's widespread use of radar and aircraft carriers clearly gives them the upper hand. Russia's mining of the Baltic Sea near Denmark and additional mining in the artic sea prevent Royal Navy from attacking the vastly inferior Russian fleet in the West. Coordinated French and British ground attacks are chewed up by superior Russian armor, including the widespread use of anti-tank heat ammo (ATL Panzerfausts). Imperial Russia has air superiority in Western Europe and decisively counter attacks along a narrow front, cutting off all the entente forces at Antwerp. France precipitously collapses and Italy joins the war against the Entente.
1946-1947 US, Britain, and Japan continue war. Entente airforces over Europe are checked by superior Russian fighters, including the first operational jet squadrons. Japan loses islands, north and south of their home islands from Russian "island hopping" campaigns. The Russian airfoce beings mining Japanese ports, leading to their capitualtion in 1947. Combined US-Royal navy maneuvers in the Pacific are defeated by qualitatively superior Russian fleet (which has many more aircraft carriers.) Hawaii is occupied by Russia. US-Canadian-British attempts to retake Alaska fail due to logistics.
1948 Russia drops an Atomic bomb on both London and San Francisco. Immediately Entente comes to terms.