1900s - Boxer Rebellion
1910s - Assassination of Franz Ferdinand
1920s - Stock market crash
1930s - German invasion of Poland
1940s - Atomic bombings of Hiroshima and Nagasaki
1950s - Suez Canal Crisis
1960s - Moon landing
1970s - Soviet invasion of Afghanistan
1980s - Tianamen Square protests
1990s - Collapse of the Soviet Union
2000s - 9/11 attacks
2010s - Brexit

Suez Canal Crisis over Sputnik's launch?

DNA's discovery is another big one for 1950s.

Right Sputnik should be #1 for the 1950s.

80s - NES
90s - SNES
00s - Wii
10s - Switch

Life was insignificant before the 80s.

Could make a case for the incredibly progress of medicine. Smallpox, measles, polio, whooping cough, diphtheria, cholera, typhus, etc. use to be major issues killing millions.

Brexit ? Really ? Who cares about what 52% of english peasants decided ?

Because I consider it the first major populist victory. Since then Trump has become president and Giuseppe Conte is the prime minister of Italy.

1900's I would have said "flight". 2000's had some of the worst natural disasters in history, would have put several of them above 9/11. e.g. the boxing day tsunami that killed approximately a quarter of a million people.

I would have said the "Machtergreifung", aka when Hitler got in power in 1933 over Poland 1939, since that's the point that started it all.

Yeah, that one really doesn't fit

Definitely Flight for the 1900's. However, 9/11 had way more far-reaching consequences worldwide than the tsunami (or any other natural disaster) had. Not even Katrina could fit, as it just went back to the status quo afterwards and couldn't convince the US to stay in the Paris agreement.