As NATO leaders meet in Washington this weekend to celebrate the Western alliance's 50th anniversary, a specter stalks the feast.
The unfolding tragedy in Kosovo, and the North Atlantic Treaty Organization's bombing campaign to reverse the "ethnic cleansing" of ethnic Albanian Kosovars, looms large over the festivities.
But the month-long war has also yielded valuable signposts for NATO as it plots its course into the 21st century, say alliance planners and diplomats.
"Kosovo adds a lot of realism to the theory," says one diplomat here. "The Balkans are a laboratory where a lot of the thinking [about NATO's future] is being tested."
And tested hard. The military parades and public displays that had been planned for the Washington summit have been canceled, in light of the fact that the Kosovo campaign offers little to celebrate. NATO's bombs (report from the strike zone, page 7) appear to have accelerated Yugoslav President Slobodan Milosevic's eviction of Albanian Kosovars, and the Serb leader is showing no signs yet of backing down.
After winning the cold war without firing a shot in anger, NATO has spent much of the past decade trying to work out what to do, now that the Soviet enemy no longer exists. Wars in the Balkans - first in Bosnia, now in Kosovo - have suggested an answer.
Rather than being an alliance for self-defense, fighting only on its own soil, and only in the event that a member state came under attack, NATO is transforming itself into "an alliance interested in a broad idea of security, with a commitment to conflict prevention and peacekeeping," said a top NATO official this week.
But this answer has thrown up new questions that have often divided the 19 alliance governments as they have hammered out a new strategic concept to be unveiled Friday.
For a start, should NATO reach beyond its original geographical confines, described in its founding treaty as "the North Atlantic area"?
To an extent, Kosovo answers that. The alliance has shown it is prepared to undertake "out of area" operations and in the future intends to act "in the Euro-Atlantic area and its periphery," in the words of a European NATO diplomat who, like others interviewed for this story, declined to be named.
How far that periphery stretches - into the Middle East, for example, as the US would like - is left undefined. But "the alliance does not see itself as some kind of global policeman" - a role many European nations feared Washington had planned for it - says the top NATO official.
The debate over when NATO should act, however, is continuing up until the last momoment before the summit.
UNDER its founding treaty, NATO recognizes the United Nations Security Council's "primary responsibility ... for the maintenance of international peace and security." But the Kosovo campaign has thrown that into doubt, since the allies launched the war without a specific UN mandate to do so.
How exactly this weekend's Washington Declaration will phrase NATO's future intentions is still unclear, with the French fighting hard to avoid undermining the United Nations, and the US insisting that the alliance should make clear its readiness to act unilaterally under certain circumstances - a view that seems likely to prevail.
This, however, risks angering the Russians even more than they are already angered by NATO's war against their Slav cousins, the Serbs.
Events in Kosovo have thrown into relief the effects of NATO's recent expansion into former Warsaw Pact territory, which always unnerved the Kremlin. Moscow has broken off formal relations with NATO since the bombing began, bitter at what it calls NATO's hollow promises that the alliance was purely defensive and posed no threat to any outside country.
At the same time, however, Eastern European countries still eager to join NATO have been trying to be helpful to the alliance in the current campaign, opening up their airspace and offering other facilities.
On the military front, Operation Allied Force has given a boost to US efforts to encourage European armies to modernize and reequip to cope with new missions.
This weekend's summit will formally launch the US-inspired Defense Capability Initiative, designed to make European military forces more mobile, more flexible, and better able to fight far from home.
The conflict in Kosovo has highlighted how "the larger the operation becomes, the larger the US share of it," points out the European NATO diplomat. "The Europeans quickly come to the limits of what they can do because they have old-fashioned forces" structured to fight a defensive war at home against the Soviets, while the US military was always designed and equipped to fight a long way from base.
"Kosovo has underscored the disproportionate role of US forces and the European allies need to redress this," says another senior NATO diplomat.
While it will take several years to reconfigure European armed forces, "in the Kosovo operation we've seen all the problems" that NATO forces will face in the sort of peacekeeping or peace-enforcement missions around the unstable edges of Europe that planners forsee, according to one alliance military source.
These problems include rapid-enough troop deployment, international logistics, a shortage of troops when the operation is functioning on several fronts, and difficulties in collating intelligence, the source says.
More fundamentally, another senior NATO diplomat argues, the West's experience of Kosovo, coming on top of events in Bosnia, shows that "we have to improve crisis prevention. That has to be a key issue in coming years, but it takes a crisis such as this one to convince everybody of this."
In the meantime, says an alliance planner, "theory is racing to catch up with reality. We're doing this on the run."