There is a Reuters story quoting a survey suggesting that the recession could trigger a general increase in violence around the world. As is always important in these kind of claims, we need to be sure that correlation between two things – violence and economic uncertainty – is not being conflated with causation. Consider: Saddam Hussein invaded Kuwait in the early 1990s when the world, in general, was quite prosperous, albeit coming out of a short recession in countries such as the US and UK, when the price of oil had also been falling. The violence that broke out in the MEast later in parts of Africa (think Sudan, think USS Cole) took place in the middle to late-1990s, a period when emerging market economies were generally on the rise. The exceptions may prove the rule: what I think is true is that places that are felt, rightly or wrongly, to be unfairly excluded from a global prosperity are often likely to be unstable, and quite violent, but not always.
In fact, it is even arguable that greater prosperity might even cause some forms of violence if reactionary/religious groups regard such wealth as a defilement of whatever it is they want to protect. (I happen to think that explains why some anti-globalisation folk are often, in essence, reactionary snobs). That in part explains the argument of those who said that the West was attacked on 9/11 not for its supposed transgressions in the Middle East, but for its wealth and freedom per se.
Where I think economics does play a more direct role is where you have regimes that are financially busted, with few remaining resources, and where they greedily, and desperately, eye other, resource-rich nations nearby. That explains some, but not all, military campaigns. As in the case of Japan during the 1930s, a hunger for raw materials, coupled with a militaristic ruling ideology and elite, led to the Japanese conquests in parts of East Asia and the Pacific Rim. The same happened with Argentina and its invasion of the Falklands Islands in 1982 (the islands are supposedly close to some very big oil reserves). Ceasar’s conquest of Gaul had a partly economic incentive (all that gold, slaves, etc). And so on.
There may also be some evidence that the more prosperous we are, the more tolerant we are, too. In fact tolerance, which is allied to liberty, and prosperity, are faces of the same coin. In the minds of the great Victorian champions of free trade, such as Richard Cobden and John Bright, free trade and peace went hand in hand. A bit naive, maybe – trade routes need to be protected against thieves and thugs – but it is a view based on an essentially benign view of how most of us live our lives, given half a chance.