History and War

"War is one of the constants of history, and has not yet diminished with civilization or democracy. In the last 3,421 years of recorded history, only 268 have seen no war. We have acknowledged war as at present the ultimate form of competition and natural selection in the human species. "Polemos pater panton," said Heracleitus; war, or competition, is the father of all things, the potent source of ideas, inventions, institutions, and states. Peace is an unstable equilibrium, which can be preserved only by acknowledged supremacy or equal power.
The causes of war are the same as the causes of competition among individuals: acquisitiveness, pugnacity, and pride; the desire for food, land, materials, fuels, mastery. The state has our instincts without our restrains. The individual submits to restrains laid upon him by morals and laws, and agrees to replace combat with conference because the sate guarantees him basic protection in his life, property, and legal rights. The state itself acknowledges no substantial restraints, either because it is strong enough to defy any interference with its will or because there is no superstate to offer it basic protection, and no international law or moral code wielding effective force.
In the individual, pride gives added vigor in the competitions of life; in the state, nationalism gives added force in diplomacy and war."- Will and Ariel Durant The Lessons of History