839. Ohio by Crosby, Stills, Nash, and Young (1970)

"Ohio" was inspired by the Kent State Massacre on May 4, 1970. At the time, American campuses were hotbeds of antiwar sentiment. Kent State students protested the Vietnam War leading to some violence and arson. The Ohio National Guard was called in to maintain order. On May 4, 2000 gathered to protest and the guard moved to disperse the crowd. They clashed with the protesters and eventually opened fire. The gunfire killed four.

http://www.youtube.com/watch?v=GI7-m919ynU