A “rare act in the great madness of this war” was how forty-five-year-old historian Howard Zinn described North Vietnam’s decision to release three American pilots during the Tet Offensive. Standing beside Jesuit priest, poet, and anti-war activist Daniel Berrigan in front of a room full of US reporters, Zinn read from one of his notebooks and declared their recent trip to Hanoi a success. The two anti-war activists met with the North Vietnamese government in February 1968 and helped transport the three prisoners back to the United States.

The exchange was largely symbolic but was an extension of his radical internationalism and opposition to foreign wars. Reexamining his provocative trips behind enemy lines during the Vietnam War — on what would have been his hundredth birthday today — serves as a reminder that Zinn was both an incredibly productive progressive historian and a persistent critic of US empire.

Zinn was the rare left historian who infiltrated American popular culture. But he is still mostly known for debunking myths related to European colonialism and the nation’s founding.