We take certain things in history for granted: Western civilization's ancient Greek origins, Rome's stunning domination of the world for hundreds of years or the democracies which have sprung up all over the world etc.
But the things that seem natural now in retrospect (ancient Greek city-states' progressive concepts, Rome's pragmatism and efficiency which also translated to the military plane, democracy's widespread adoption), might not have happened at all!
Because the fate of millions and humanity as a whole can be altered irrevocably by the actions of a small group of individuals or even just one individual. For example, there is a very strong possibility that Nazi Germany would have won the war if it had not chosen to invade Russia, a decision made by Hitler and a handful of his closest that resulted in crippling economic and political consequences for his regime, along with one of the most disastrous military campaign in history.
