John F. Kennedy was assassinated in 1963. His successor, Lyndon Johnson, kept McNamara as Defense Secretary. He became a major leader of the Vietnam war, and he and General William Westmoreland were the two biggest leaders in the American military during the war. In order to stop the communists from taking over Vietnam, McNamara sent more troops to the country. Over a number of years this stopped the North Vietnamese Army from winning the war, but as large amounts of American soldiers were killed the war became very unpopular with the people. He and the president strongly disagreed on troop levels - McNamara wanted to stop the increase in troops but Johnson wanted to send more over. McNamara resigned from the Defense Department in 1968. Johnson did not run for reelection that year and the election was won by Richard Nixon, who ran on a promise to end the war. Nixon signed a peace treaty in 1973, but the North Vietnamese would eventually win the war after the US pulled out.