War is a fact of human nature. As long as we exist, it exists. That's how the argument goes. But longtime Scientific American writer John Horgan disagrees. Applying the scientific method to war leads Horgan to a radical conclusion: biologically speaking, we are just as likely to be peaceful as violent. War is not preordained, and furthermore, it should be thought of as a solvable, scientific problem—like curing cancer. But war and cancer differ in at least one crucial way: whereas cancer is a stubborn aspect of nature, war is our creation. It's our choice whether to unmake it or not.