Final answer:
The protestors were killed by the National Guard at Kent State University in Ohio on May 4, 1970. Four students were killed, and nine wounded during an antiwar demonstration. A similar event occurred at Jackson State College, resulting in two deaths and twelve injuries.
Step-by-step explanation:
The National Guard killed protestors on the college campus of Kent State University in Ohio. On May 4, 1970, during a demonstration against the Vietnam War and the invasion of Cambodia, 77 National Guard members approached the students. Despite attempts to disperse the crowd, the situation escalated, and the guardsmen opened fire, which resulted in the tragic death of four students and wounding of nine others.
Additionally, a similar event occurred on May 15, 1970, at Jackson State College, where another protest led to the killing of two individuals and the wounding of twelve by police officers. The incident at Kent State University became a pivotal event in the antiwar movement and significantly increased polarization within the United States regarding the Vietnam War.