Student-led protests in response to US engagement in the Vietnam War mounted in the 1960s and led to a group called the Weather Underground that believed in direct confrontation with the state.
Almost 56 years to the day after the anti-war protests in 1968, New York City police evicted Columbia University students from an on-campus occupation.
While most colleges and universities have their own police units, some schools, like Columbia University, have only private security − and then can call in outside police when they feel it is needed.