1970, against North Vietnamese bases in the east of the country, and further protests erupted against perceived expansion of the conflict, which resulted in Ohio National Guardsmen killing four unarmed students at Kent State University. Nixon's responses to protesters included an impromptu, early morning meeting with them at the Lincoln Memorial on May 9, 1970. Nixon's campaign promise to curb the war, contrasted with the escalated bombing, led to claims that Nixon had a "credibility gap" on the issue. It is estimated that between 50,000 and 150,000 people were killed during the bombing of Cambodia between 1970 and 1973. In 1971, excerpts from the "Pentagon Papers", which had been leaked by Daniel Ellsberg, were published by The New York Times and The Washington Post. When news of the leak first appeared, Nixon was inclined to do nothing; the Papers, a history of United States' involvement in Vietnam, mostly concerned the lies of prior administrations and contained few real revelations. He was persuaded by Kissinger that the Papers were more harmful than they appeared, and the President tried to prevent publication, but the Supreme Court ruled in favor of the newspapers. As U.S. troop withdrawals continued, conscription was phased out by 1973, and the armed forces became all-volunteer. After years of fighting, the Paris Peace Accords were signed at the beginning of 1973. The agreement implemented a cease fire and allowed for the withdrawal of remaining American troops without requiring withdrawal of the 160,000 North Vietnam Army regulars located in the South. Once American combat support ended, there was a brief truce, before fighting resumed, and North Vietnam conquered South Vietnam in 1975. Latin American policy Nixon had been a firm supporter of Kennedy during the 1961 Bay of Pigs Invasion and 1962 Cuban Missile Crisis. On taking office in 1969, he stepped up covert operations against Cuba and its president, Fidel Castro. He maintained close relations with the Cuban-American exile community through his friend, Bebe Rebozo, who often suggested ways of irritating Castro. The Soviets and Cubans became concerned, fearing Nixon might attack Cuba and break the understanding between Kennedy and Khrushchev that ended the missile crisis. In August 1970, the Soviets asked Nixon to reaffirm the understanding, which he did, despite his hard line against Castro. The process was not completed before the Soviets began expanding their base at the Cuban port of Cienfuegos in October 1970. A minor