I joined the anti-Vietnam War movement as an 18-year-old freshman at Columbia University. It was the fall of 1965, just months after the United States began sending ground combat troops to Southeast Asia. The older members of the Columbia chapter of Students for a Democratic Society explained to me that unlike World War II, Vietnam was an imperial war, a war of occupation whose purpose was the repression of a national liberation movement. We were a small group then, but over the next three years SDS became a critical part of a larger antiwar coalition. Our anger mounted, our protests...