|An image of the First World War|
[A] suspicion arises that the holocaust of modern war is the safety-valve of an economic system where production, pursued as an end in itself and getting out of touch with consumption, has loaded the world with unwanted goods. But this cannot be the explanation [for modern war], for if these goods were unwanted, their destruction, like that of a target in gunnery practice, would not be an act of war. The militarist must value his children and his property, or the Moloch to whom he sacrifices them would not be appeased. The sacrifice is the self-torture of an insane civilization. 
Alike economically and politically, therefore, the militarism which is so deeply rooted in our modern political system is a form of insanity. To represent war as the ultimate and highest end of the state is to misconceive both the relation between war and wealth, and the relation between war and policy. [311-312]
Warfare, the organized warfare of states as distinct from mere personal violence, is not a primitive human institution. It was invented at relatively high stage of civilization, and was invented as a cheap and easy way of acquiring riches. 
To economic ends, political ends may be added: domination may be desired for its own sake, and wars of conquest, as distinct from wars of exploitation, may be fought. Or a war may be wages for religious motives, the glory of God, not the glory of man, being the prize. The destructiveness of economic or acquisitive warfare is limited by the need to make a profit out of it; hence, the conqueror is not willing to spend more than he is likely to get, nor is likely to bleed his victims to the point of exhaustion. . . Political warfare is crueler and more destructive: but even here a limit is set to its destructiveness by the fact that a conqueror would, in general, rather rule over a tolerably prosperous people than over a wilderness. [312-313] Religious warfare is the cruelest of all, because the issues at stake being purely spiritual there is no care for material welfare, or even for the life of the body: the very existence of infidels is unpleasing to God and their complete destruction is meritorious. Since the seventeenth century, all wars between civilized peoples have tended to be at bottom wars of religion, the cultural ideals for which people nowadays mostly profess to fight being in te nature of religious principles, however little they may associate themselves with deities and temples. Not only do they resemble religious wars in being fought for sprititual ideals, they resemble them in their absolute ruthlessness and in the fact that they recognize no limit to their destructiveness of life or property. Thus in their general character they resemble religious wars: but they differ from religious wars in that they set before themselves no definite aim, and therefore have no definite criterion of victory or defeat. 
[I]n spite of the of the vaguely religious or quasi-religious character of modern warfare, it is not truly religious, for, so far from having a religious motive, it has no motive at all. It is notorious that in modern war there are no victors. The reason for this is now clear. In order that someone may win a war, the war must be about something: there must be aims on both sides, and a question to be settled by fighting. In modern war, there are no such conditions. There are, therefore, no victors and no vanquished: only combatants seared alike in the furnace they have conspired to light, all exhausted, though exhausted in varying degrees. [313-314]
Some points to ponder:
- Collingwood wrote this having lived during the First World War, albeit working in the Admiralty and not serving at the front. The First World War, of a century ago, was a cataclysmic event for Europe. It shattered a century of relative (Great Power) peace that has existed since the Napoleonic Wars. And in 1936, all aspirations not to the contrary, the prospect of war was again looming on the horizon.
- Note that the U.S. is engaged in a "War on Terror," although we no longer use that nonsensical nomenclature. We are locked in a battle with a 'jihad' that makes no sense from an economic or political perspective. Thus, neither side can define victory (see Afghanistan) or place a limit on the nature and extent of the warfare. The U.S. resorted to torture, assassination, and indefinite incarceration in defiance of established Western norms, rationalizing these practices as necessary to succeed in the this (un)holy war.
- A point of curiosity for intellectual historians: Keynes published his General Theory in February 1936. Had Collingwood read it? Collingwood's reference to the problem of over-production certainly notes the problem a problem that the addressed.