On April 30, 1970, President Richard Nixon announced that U.S. troops had invaded Cambodia. Students viewed this as an escalation of the Vietnam War after Nixon had vowed troop withdrawal, and Kent State students joined protests occurring nationwide. On May 1, they symbolically buried the U.S. Constitution, saying Nixon had “murdered” it. Black United Students rallied to discuss harsh treatment of demonstrators elsewhere and warned members to avoid campus gatherings. On May 4 at noon, Ohio National Guard troops advanced on a protest rally, and twenty minutes later guardsmen killed four students and wounded nine others. College students nationwide responded with the largest student protest strike in U.S. history. President Jimmy Carter later reflected that from Vietnam to Cambodia, from Los Angeles to Memphis, from Kent State to the Watergate, the American spirit suffered under one shock after another and the confidence of the people was deeply shaken.