We may yet work up to some serious shooting war, or maybe some acts of urban genocide committed with rogue nuclear weapons. But if that were the case, why would we call that "9/11"? If Washington disappeared in a mushroom cloud, we'd give that huge event a different name.
Humans are very aggressive and scrappy, and go to war at the drop of a hat. However, a standard land war is no longer going to work as it is no longer technically possible.
War as Napoleon knew it just not possible any more. However, we're very unlikely to accept or recognize "world peace" even when we get it.
