War may indeed be a continuation of politics by other means. But as cataclysms, shocks and surprises accumulate, wars may often be most comfortably understood as continuations of other wars. Wars make most sense when they resemble wars already known. So generals always fight the last war, protesters object to the last war and debates rage over which last war is being resurrected. Right now the main contenders are Vietnam — with its heritage of mistrust, protest and murky, futile death — and World War II — with its heritage of virtue, necessity and high heroism. These models offer seemingly...