I would say the contraceptive pill.

Australia was greatly influenced by American events in the 1960's, especially protests about being involved in the Vietnam war and equal pay for women. During the 1960's, many Americans protested to demand an end to the unfair treatment of black citizens, an end to the war in Vietnam and for equal pay for women. Australians were shocked by the assassinations of President Kennedy and later his brother. By the middle of the nineteen sixties, it had become almost impossible for President Lyndon Johnson to leave the White House without facing protesters against the war in Vietnam and in 1968, Johnson announced that he would not run for another term in office. In addition to President Kennedy, 2 other influential Americans were murdered during the 1960's. Civil rights leader Martin Luther King Junior was shot in Memphis, Tennessee, in 1968. Several weeks later, Robert Kennedy -- John Kennedy's brother -- was shot in Los Angeles, California. He was campaigning to win his party's nomination for president. The two murders resulted in riots in cities across America.