The world once again has a global policeman. The six Canadian fighter jets and many more warships and aircraft that are being sent to Libya are taking part in a most controversial form of warfare: the bombing of a sovereign state to protect its people from their ruler.
As any cop will tell you, police operations are rarely quick, easy, clean or surgical. The United Nations Security Council resolution reached Thursday night is far more than a "no-fly zone," as it authorizes UN members to take action against any of Moammar Gadhafi's air or ground forces to stop his killing of Libyans. We have now taken a side in this war.
What the resolution doesn't say - but what it certainly means - is that, after the conflict has ended, the world will be playing an active role in Libya's transition to democracy, probably for some time to come, possibly for years.
The Arab Spring, in other words, is now our business. This could be a history-changing moment, in which the U.S. and its allies are once again seen in much of the Muslim world as supporters of the people. But there are many ways it could go wrong. We need to learn from the few times this has been tried.
You know what they say about global policemen: They're never there when you need them, always there when you don't. There are many who feel President Barack Obama waited too long to commit the U.S. to taking military action to stop Colonel Gadhafi, and to support a democracy movement that seemed to reflect core U.S. values. In this view, he dithered.
But there were even more compelling reasons for him to avoid rushing into Libya - even though the leaders of the anti-Gadhafi rebels, and many of the world's humanitarians, were begging Washington to take action.
This was done the right way: through a Security Council resolution, following the rules the world agreed on after the horrors of the 20th century, in a motion initiated by Lebanon and supported by several key Muslim nations (and with active military involvement by several Arab states). It was worth waiting to get it right.
If the Iraq war had been organized this way, as an action of the whole world, we might remember it as a democratic and humanitarian success. But it was the lack of such co-operation in Iraq - and the complete lack of any intelligent action once the brief period of regime-change conflict was over, leading to a post-conflict catastrophe - that meant Washington could not possibly have been the leader on Libya. The sight of American soldiers on Arab soil would be sure to provoke the worst sort of response across the region, and would be used by other Arab dictators as a rationale for crushing democracy movements.
Could that perception change? Yes. We forget how recently things were different.
The second time a no-fly zone was authorized, after the one to protect the Kurds in Iraq in 1991, was to protect a largely Muslim population of Bosnia from being slaughtered by a largely Christian force bent on putting an ethnic Serbian stamp on the former Yugoslavia.
That was repeated in 1999 - without Security Council authorization - when NATO bombed Belgrade to protect the mainly Muslim population of Kosovo from Slobodan Milosevic's forces; it worked, and was followed by vital support to Serbia's democracy movement, which unseated Mr. Milosevic the following year.
For a while, the U.S. and its allies were praised as defenders of Muslims; the Kosovar capital of Pristina still has a main street named Bill Clinton Boulevard in honour of their hero. It seemed that the quick, sharp international action was the formula for global peace.
It was the confidence created by these comparatively successful (if tragically late) interventions that led many world leaders to back the ill-considered 2003 invasion of Iraq (whose 1991 no-fly zone had been an expensive failure) and to overextend themselves in Afghanistan. The wars of the 2000s taught us that quick regime-change strikes can become tragedies of epic proportion, not to mention nearly destroy the image of the U.S. and its allies.
History has turned with astonishing speed. In Benghazi on Thursday, young Arabs waved U.S. and French flags in joy, welcoming Western planes as liberators. It's a great moment, and the world ought to seize it - but we should remember how fast, and how badly, things can turn.