On April 30, 1970, President Richard Nixon (1913–1994) announced to the nation that he had sent American forces into the neutral country of Cambodia. His reason was to "clean out" Communist base camps that were being used for attacks against U.S. troops in Vietnam during the Vietnam War (1954–75). Antiwar sentiment on the college campuses, which had been relatively quiet for months, exploded in response to the news. Although Nixon was emphasizing the protection of American troops and the brief nature of the incursion, outraged opponents of the war focused on the neutrality of Cambodia and what seemed to be the expansion of the fighting into yet another country. Marches, rallies, and demonstrations of all sorts erupted on campuses across the nation.

Grief prevailed in the aftermath of the confrontation with the Ohio National Guard on the Kent State University campus, where, on May 4, 1970, four students were...