Here is an article discussing a book on a fascinating event in the history of WWI. This event underlines the fact that war is solely the consequence of the existence of the state. The state is war. I am reading Machiavelli's The Prince and he inadvertently makes the case that the state is war in section XIV "What a Prince Should Do Regarding the Military", where he says:
Thus a prince should have no other object, nor any other thought, nor take anything else as his art but that of war and its orders and discipline; for that is the only art which is of concern to one who commands. And it is of such virtue that not only does it maintain those who have been born princes but many times it enables men of private fortune to rise to that rank; and on the contrary, one sees that when princes have thought more of amenities than of arms, they have lost their states. And the first cause that makes you lose it is the neglect of this art; and the cause that enables you to acquire it is to be a professional in this art.
War is the health of the state. The state is war. World peace? Eradicate the state.