Sam thinks we might be less willing to go to war in future because we value human life more than we used to. It's a beguiling argument, because it appeals to an instinctive conviction that we are somehow wiser and better people than our ancestors. Actually, I'm a bit surprised that a staunch Oakeshottian like Sam is beguiled by such Whiggish optimism, but the argument deserves to be examined on its merits. Two points, then.

First, I'm not sure the empirical evidence, such as it is, supports the view that we value human life more now than our predecessors did. I keep on being surprised by how willing modern societies are to accept military casualties in marginal causes: consider the Canadians in Afghanistan, now with over 140 KIA. Or indeed how little the loss of 11 of our own people has weighed in thinking here about Afghanistan.

Conversely, it's hard to say that our ancestors did not value the lives of others as much as we do today. The weighing of individual sacrifice against collective purpose has been seen as the essence and tragedy of war since the beginning of politics. That is why the mainspring of Aeschylus' account of the Trojan War is not a great battle but Agamemnon's decision to sacrifice his own daughter for a wind to take the Greeks to war. 

Nor do I think economics has much to do with this: I cannot agree with Sam that the money we spend educating our soldiers equipping them makes any difference to how much we value their lives. 

Second, I'm not sure I share Sam's belief that decisions for war are made by people slowly and carefully and weighing costs against benefits. It would be nice if they were, because that would allow us to predict strategic behaviour the way we predict economic behaviour – by presuming informed choices by rational individuals pursuing their long-term interests. I'd defer to Mark Thirlwell on how well this model works in economics; it certainly doesn't help us explain choices for war.

There are several reasons for this:

  • While Sam is right that decisions to build forces are taken slowly and deliberately, decisions to use them in war are most often taken quickly and under pressure.
  • The choice for war is often the last step on a long road of escalating strategic competition. The first steps on that road always seem harmless enough, but each one brings closer the point there seems no choice but for war, whatever the cost. So one might say that we do sometimes choose war slowly, step by step, but we do not know that is what we are doing until the last step, when it seems impossible to do anything else.
  • The decisions we take at those fateful moments are seldom informed by a clear understanding of the costs ahead. Even at the last moment, would anyone have chosen war in 1914 if they had known that they were heading not for Sedan but the Somme (pictured)? Would Bush have chosen war in 2003 if he had known he was heading for Fallujah? Would anyone think it would be worth the US and China fighting over Taiwan if they understood how easily it could lead to nuclear war between them?  
  • Finally, the decisions for war are made by groups, not individuals; and groups behave oddly, especially under stress. Think of the scene in Thirteen Days where Adlai Stephenson earns the scorn of his colleagues by suggesting that a deal with Moscow might be better than nuclear war.  

In the end, if we argue that the costs of war today make it unthinkable, we must explain how the costs of a global nuclear exchange in the Cold War did not seem to make war unthinkable only 25 years ago. Do we weigh the costs of economic disruption today more highly than decision-makers in 1985 weighed the costs of 100 million dead, or are we just being forgetful?

Actually, I think the focus on shifting views of the costs of war is misleading. Something else is at work here. I do not think we rate the costs of war any higher than we used to, but we do find it harder to imagine a strategic challenge which would justify the costs of major war no matter how they are calculated. 

In other words, the costs of war have not grown, but the reasons for war seem to have shrunk. And that is because, unlike the Cold Warriors, we do not envisage a serious challenge to the international order that underpins our security. If we did envisage a challenge to that order, our views on the costs and risks of major war might change.

And that, of course, is why the possibility of future major war arises. I do not rate that risk very high, because, like Michael and Sam, I think the costs of war do place a huge constraint on strategic competition. But the risk remains, and it will grow if the stable order of recent decades erodes as economic weight and strategic power shift. 

This is a dangerous moment in which concern about the future international order means that the imperatives for war could again rise, notwithstanding the appalling costs. Unless we acknowledge that risk, we will not work hard enough to avoid it. And we cannot afford not to work hard, because we cannot simply rely on globalisation to keep the world peaceful for us over the next few decades.

Photo by Flickr user seabjack, used under a Creative Commons license.