1950, both the Soviets and Chinese intervene in Korea. Once fighting breaks out, the United States starts preparing an army to send to Europe. Stalin reacts and invades Europe, taking Greece, Germany and the Lowlands with heavy fighting taking place in France and the Italian Alps. Eventually both countries fall after breakthroughs, Turkey is also taken.
The UN forces in Korea are overwhelmed, European governments once again form governments in exile.
Fighting is fiercest in Northern Europe, where Norway and Sweden are heavily reinforced to fight the Soviets. Bombers based in Southern Sweden attack forces in occupied Germany and the rest of Europe.
Outside of Europe is the Middle East where British and American formations fight against the Soviets who are moving down the peninsula to take the Suez Canal and capture oil fields around the Gulf.
In South-East Asia Chinese forces have invaded Vietnam to support Communist guerrillas against French, Australian, British and American forces to have occupied the country and are using it as a base to invade China. In Japan and Taiwan bombers are based to pound Chinese and Eastern Russian cities, napalm is heavily used.
I'm not even sure who would win this war, I don't believe either side has the resources to fully defeat the other.