First, it's important to note that rape and war didn't always go together. For instance, European colonists wrote astonished letters home about how "even these savages" -- by which they meant the residents of this continent they were invading -- didn't rape, not even their women prisoners. But those were wars of self-defense. If you're going to get groups of men to risk their humanity, health, and lives in wars of offense, the traditional way is not to pay them a lot, but to addict them to the "cult of masculinity." You have to convince them they're not "real men" unless they kill and conquer. And, at its most basic, "masculine" means not being "feminine." On a continuum, it means controlling women, conquering women, raping women, even with objects: bottles and broom handles in "peacetime" here, and gun barrels and knives in Bosnia or Congo. There's a reason why it's a truism that rape is not sex, it's violence.

It's also true that men may rape in groups out of social pressure to prove their "masculinity" -- in peacetime, too -- but gang mentality is a way of life in war. Military officers sometimes order men to rape as proof of loyalty and shared culpability. Some men express regret and say they wouldn't have raped without group pressure. Also the group hatred war requires means humiliating enemies by raping "their" women, implanting sperm, taking over their means of reproduction, wiping out the enemy race or ethnicity. Cultures that put all "honor" in the purity of "their" women -- and keep women weak -- are actually setting them up as targets.

Even in peacetime, the "cult of masculinity" is so powerful that men commit crimes in which they have absolutely nothing to gain and everything to lose: "senseless" killings like those in schools and post offices, serial murders, domestic violence, stalking, killing their wives and children and then killing themselves. They're not hate crimes because they don't hate the people they kill -- but those people symbolize their lack of control, and so are killing the "masculinity" on which their whole sense of self depends. In interviews, such men often describe themselves as victims because they believe they should have been allowed to have control. I think we should call such crimes "supremacy crimes."

What do you say to people who assert that sexualized violence is a "natural" part of conflict?

I try to think of something from the past that was also thought to be "natural," and wasn't. For instance, violence was once a "natural" part of childrearing, as in, "Spare the rod, spoil the child." It was also "natural" in marriage, as in, "Wives and bells must be struck regularly." It was "natural" in religion, as in flagellating and starving the flesh to free the spirit.

Or I quote Olof Palme, the great former prime minister of Sweden, who said that gender roles are the deepest cause of violence on earth, and it's up to governments to humanize them. Gender roles may give us our first idea that it's okay for one group to eat and the other to cook, one to talk and the other to listen, one to order and the other to obey, one to be subject and one as object. The most shared characteristic of original societies in which violence was only for self-defense, not armies -- and of the most egalitarian societies now -- is that gender roles are fluid and not polarized.