On this day in 1918, the Sedition Act of 1918 was passed by the US Congress, making criticism of the government during wartime an imprisonable offense. It would be repealed less than two years later.
On this day in 1966, the Communist Party of China issued the "May 16 Notice", marking the beginning of the Cultural Revolution.
On this day in 1975, India annexed Sikkim after the mountain state expressed in a referendum that it was in favor of merging with India.
On this day in 2011, STS-134 launched from the Kennedy Space Center on the final flight for Space Shuttle Endeavour.