LANSING, Mich. — Whatever drove a gunman to unleash terror in Marco Díaz-Muñoz’s Michigan State University classroom last year started long before the man picked up a gun or stepped into Berkey Hall. Díaz-Muñoz, an assistant professor in the Department of Romance and Classical Studies whose students were among those wounded and killed in the Feb. 13, 2023, shooting, doesn’t lay the blame at the gunman’s feet. Two of the three students killed were in his Berkey Hall classroom as well as the five students who were seriously wounded. Mass violence, like that which unfolded in front of him, germin…