The first interview I did with Gene Sharp was for a foreign-policy roundtable back in 2003. He wrote afterward to say he mostly liked the piece but I should please not call him a pacifist again.

This took me by surprise. Sharp, who died last week at age 90, had been a draft resister during the Korean War and an editor of Peace News. He had studied Gandhi's life and work for strategic insights, and he had dedicated his career to showing how dictatorships could be overthrown and invaders repelled nonviolently. That all sounded pretty pacifist to me. What I didn't appreciate was how much Sharp associated the term pacifism with a purely ethical position, and how frustrated he had gotten with so many of the people who embraced the p-word. "I don't condemn people who believe in nonviolence as a way of life," he told me in one of our later interviews, this one conducted as the Arab Spring was surging. "For them, that may be the best they can do. And there are other people who have been witnessing and protesting and being true to their beliefs, who want to know how they can do this most effectively. But they don't always grasp the importance of doing more than that. Not just to witness against the wickedness of the world, but how to change the world."

Meanwhile, most of the people he was learning from weren't pacifists at all. He had searched the historical record for empirical examples of civic resistance, ranging from "rude gestures" to nonviolent strikes and mutinies, even the creation of parallel grassroots systems of governance. He discovered countless case studies all over the globe. The vast majority of people conducting these protests and revolts, he noted, were not ideological pacifists; they were figuring out tactics and strategies on the fly. Sharp, in turn, focused more on how they were fighting than what they were fighting for. In the battle over Jim Crow, his sympathies were with the civil rights movement—he had taken part in a sit-in himself—but when the segregationists used a nonviolent tactic, he made sure to examine that too. After all, someone else might find it useful.

Sharp compiled a long list of those methods, and he developed a theory of power to explain why they worked (and why they sometimes didn't). It's a remarkable body of writing: Sharp is, I think, one of the most essential and underappreciated political thinkers of the late 20th and early 21st centuries. No mere armchair theorist, he then set about sharing his findings with dissidents everywhere from Burma to the West Bank. When the next generation of nonviolent rebels came along, they were deeply in his debt. (After the Baltic states gained their independence, one Lithuanian defense minister said of Sharp's Civilian-Based Defense, "I would rather have this book than the nuclear bomb.")

I'm pretty certain that Sharp never lost the moral commitments that led him to pacifism (and anarchism) in his youth. But his vision really was much larger than pacifism, and I understand why he didn't like the label. Besides, the pacifists weren't sure they wanted him either. My favorite Gene Sharp story is the time he gave a talk about nonviolent resistance to foreign invasions. "Someone in the audience was very shocked," Sharp recalled, "and accused me: 'All you are doing is taking the violence out of war!'"