Peace impossible without war?

Aren't human beings too imperfect to exist peacefully without war? I mean, even if you take the view that war is evil, you have to admit it's a necessary evil. For instance, World War II. If America and Russiua had remained neutral, even when attacked, Germany would have ended up slaughtering even more Jews, and possibly taken over the world. Aren't there times that require war to create peace? In theory, peace shouldn't coexist with war. But in reality......? Would it have been more moral of us to allow millions to die while we stay at home, safe and "not involved"? Imagine how many more lives would have been taken because of our inaction...