For older folks, I would argue that Japan's attack on Pearl Harbor changed the entire world. As for myself, I wasn't alive then, so it's probably the attacks o

For older folks, I would argue that Japan's attack on Pearl Harbor changed the entire world. As for myself, I wasn't alive then, so it's probably the attacks on September 11th. They resulted in numerous wars, changed the lives of probably billions of people, changed the characterization of an entire religion, affected foreign and domestic policies, etc.