[Harpo]

I like considering the alternate histories, especially those which hinge on one person before later important events in their lives.

In the early 30s Winston Churchill was knocked down by a taxi.
When Alexander The Great was younger he was almost killed in battle.

Both of those might have died, but instead they later changed history.
When Ogadai (ruler of the Mongols and third son of Ghenghis Khan) died, the Mongols ceased their unstoppable advance westward. They would have destroyed many of the great European cities, and who knows how much of our culture would never have existed?
The Mongols went home and elected a new leader, after which they turned their attentions on China.