1905: The Theory of Relativity
1912: The Titanic sinks
1920: Women get the right to vote
1928: The discovery of Penicillin
1929: Wall Street Crash
1945: The End of World War 2
1948: The Berlin Blockade
1955: The Polio vaccine gets adopted throughout the United States
1957: The Soviet Union launches the Putnik 1 satellite
1968: The assassination of Robert F. Kennedy
1969: The Apollo Moon landing
1986: The Space Shuttle Challenger disaster
1989: The Fall of the Berlin Wall

[Source: XKCD]