The 1970 killings of protesting students by National Guardsmen at __________ caused many students to increase protest activity on Oklahoma campuses.

The killings occurred at Kent State University in Ohio on May 4, 1970, when National Guardsmen fired on students protesting the Vietnam War, killing four. The incident sparked protests at campuses across the country, including in Oklahoma. Therefore, the correct choice is Kent State University.

AI-written and checked against the verified answer.