The western alliance is now faced with doing what it tried hard to avoid - bombing Serb installations and forces in order impose a settlement of the Kosovo crisis.
It's unclear, at this point, that the NATO action will have that desired effect. The Serbs may only dig in deeper. But it's clear that if the air raids were withheld, yet again, Serbian leader Slobodan Milosevic would have a green light to sweep through the province, eliminate the Kosovar Albanian opposition, and terrorize the civilian population there.
Such a Serb blitz would only set the stage for further conflict, as the Albanians regroup and perhaps draw added support from compatriots in surrounding countries.
Just as important, it would suggest that NATO had lost all will to intervene and stop explosive conflicts in Europe. The credibility of international peacekeeping, generally, would take a direct hit.
The United States and its Western European allies have two paramount interests in Kosovo: (1) averting a humanitarian catastrophe that could send renewed refugee floods out of the Balkans and rerun ghastly scenes of massacre and ethnic cleansing; (2) quelling a conflict that could all too easily widen in scope. It's not difficult to imagine Albania, Macedonia, Greece, or Turkey being drawn into the fighting.
The humanitarian catastrophe has already begun. Refugee flows are growing in the face of the Serb offensive. The second interest, admittedly, is more speculative, but eminently possible. It would make little sense to let things run unchecked in the hope the conflict would contain itself.
Americans may ask, Why should we risk one pilot over what is clearly Europe's problem? That question has discomfiting echoes from the 1930s. What's the danger of letting Mr. Milosevic work his will unhindered in Kosovo? It would trumpet the message that tyrants can flout the intentions of the wider international community. And if that can happen right in Europe's backyard, with the security structures in place there, what hope is there elsewhere?
These dangers may not be as obvious as direct threats to allies (though NATO allies are right next door to the conflict) or threatened oil supplies. But they directly relate to stability in an ever more interdependent world.
Europe and the US already have a substantial investment in Balkans peacemaking. To back off in Kosovo would be to risk that investment - not to mention the lives of perhaps thousands of civilians - as well as future such commitments.