The Battle of Gettysburg, one of the most important battles of the American Civil War, began. 1863.

The United States, the United Kingdom, the U.S.S.R., and 59 other states signed the Nuclear Non-Proliferation Treaty in an attempt to halt the spread of nuclear weapons. 1968.

Sony began selling its Walkman, a portable cassette player; an international sensation, the device changed the way people listened to music. 1979.

The International Criminal Court—established to prosecute and adjudicate individuals accused of genocide, war crimes, and crimes against humanity—began sittings. 2002. 

The Dominion of Canada was formed this day in 1867, an event subsequently celebrated as an annual Canadian holiday (its current name, Canada Day, was adopted in 1982) marked by parades, fireworks, and the display of flags. 1867.