It would be interesting to see some empirical research on this question. Obviously it’s hard to say when a war has been “stopped” — if something never happened, how can you be sure it would have happened? But there have been a few near-misses, including the Bay of Pigs invasion and the Cuban Missile Crisis: a mid-20th century “Cuban War” is the one war that probably “should” have happened, given America’s penchant for intervention in much less likely places, but didn’t.

Unfortunately, an analysis of why the Cuban War never happened wouldn’t paint anyone in a good light: antiwar activists certainly didn’t stop the war and only external realities imposed by the superpower balance may have prevented the governing class from doing what it would have liked to do. Our own hegemony is the textbook case for “offshore balancing.” But as the Cold War also shows, superpower rivalry causes wars as well as prevents them, so there’s no answer here.

If internal political forces can stop a war, what are they? One thought experiment that comes to mind is to wonder which of the following scenarios would have been more likely to keep us out of Iraq. Scenario A: Antiwar protests along the same lines as those we actually saw, but ten times bigger. Scenario B: Jeb Bush rather than his brother is president, and Colin Powell has enough spine to tell him the war is a bad idea and he won’t sell it (maybe he’ll even resign).

Secretary of State William Jennings Bryan failed to dissuade Woodrow Wilson from going to war with Germany, but World War I was a bigger deal, with much greater pressures for intervention, than Bush’s war of choice. Could a Bryan have deterred a smarter Bush over some small war?

With all the sound and fury over Rand Paul’s endorsement of Mitt Romney, the accusation leveled against “pragmatists” is that they don’t really oppose the empire. But if pragmatism has a better chance of stopping a war than loud but feckless activism, it’s the purists who are really selling out, by pleasing themselves instead of making hard, compromising choices that might actually avert other peoples’ deaths. Don’t play that game, though: neither Bryan nor marching in the streets has much chance of succeeding, and people of good faith can try either tactic.

This is on my mind not only in light of the Rand blow-up, but also because in talking to antiwar lefties I’m always exasperated by their lack of interest in trying anything new: marches, puppets, call-in radio shows, camping out in the street, sign waving, and Jesse Jackson chants will stop the next war, won’t they, even if they didn’t stop the last half dozen? It’s not intrinsically any more absurd to think so than to think Secretary of State Chuck Hagel would do any good, but when dealing with low probabilities of success each side ought to give the other some benefit of the doubt.

Hegel I’ve never had any confidence in, but that general approach seems to me more worthwhile than the protests that have failed to accomplish anything over the last half-century. Even Cindy Sheehan contributed very little to ending the Iraq War: her 15 minutes of fame came in 2005, two years into the war, which the continued for another whopping six years. The troops only came home at last when, again, an external actor — Iraqi Prime Minister Nouri al-Maliki — defied Uncle Sam.

Sheehan almost certainly contributed to the Democrats’ takeover of Congress in 2006, but that takeover famously failed to put a stop to the conflict. There are, however, at least mechanisms by which one can imagine the elite pulling the plug on a war, while the idea that generals and diplomats are ever going to care about street protests, short of bloody insurrection, seems farfetched.