Final answer:
The Kent State University protests in 1970 were caused by opposition to President Nixon's announcement of the Cambodia Campaign, which expanded the Vietnam War.
Step-by-step explanation:
The cause for the violent student demonstrations that took place at Kent State University in 1970 was opposition to the expansion of the Vietnam War into Cambodia. This opposition was sparked by President Richard Nixon's announcement on April 30, 1970, of the bombing campaign in Cambodia, an action seen as an escalation of the conflict. The resulting anti-war protests spread across college campuses nationwide, culminating in tragedy when the Ohio National Guard fired into a crowd at Kent State University on May 4, killing four students and wounding nine.