In April 1968 Columbia SDS, led by Mark Rudd, joined Black students of the Student Afro-American Society in seizing five university buildings — against the university's secret war research for the IDA and its plan to build a gym in Harlem's Morningside Park. For a week the occupied buildings ran as communes, until the night of April 30, when a thousand police cleared them with clubs: nearly 700 arrested and some 150 injured in the largest mass arrest in the city's campus history.
A second bust in May brought the semester's arrest total past 1,100. Most charges were eventually reduced or dismissed, but dozens of students were suspended and the spectacle — echoed at campuses worldwide in 1968 — turned SDS toward the confrontation politics that split it a year later.