In terms of specific moments that changed the way we in America at least
perceive ourselves, our place in history I would offer
The Wright Brothers First flight 1903 (I think)
The Stock Market Crash 1929
Pearl Harbor 1941
The Atomic Bomb dropped on Hirsoshima and Nagasaki 1945
Univac 1946
Polio Vaccine early 1960s?
The Pill mid1960s
The first Moon landing 1969