I'll add two what-ifs, being somewhat a fan of alternate history stories.
# 1. Archduke Franz Ferdinand decides to put the roof on his motor carriage up after the first assasination attempt. Result, the assasin doesn't see the Archduke in the vehicle and never discharges his pistol into the vehicle. No WW1, no bolshevik revolution, no Soviet Union, no third reich, and the United States takes about twenty years longer to become the economic powerhouse it did in the real world.
# 2. George C. Marshall's mission to China is unsuccessful. Chang Kai Shek completes his defeat of the Chinese Communists led by Mao Tse Tung. Russia has to invest more earlier into it's defense of it's Chinese border. No Chinese intervention on behalf of the Korean communists. No Vietnam. Likely an earlier collapse of the Iron curtain in Europe.
Something tells me the DUmmies won't even think of these.