NATO, the most successful military alliance in history, is facing twin crises. Either could prove disastrous to the 26-member organization.

One crisis is Afghanistan, the front line in the global war on terror. Over the past two years, Taliban attacks have increased and become more deadly. The Afghanistan Study Group reported that 2007 was the deadliest year for American and international troops in Afghanistan since the 2001 invasion.

Last month, insurgents mounted two of the boldest attacks in years on NATO forces. In one, a squad of suicide bombers launched a failed assault on a U.S. base near the Pakistan border. In the other, 10 French paratroopers were killed in a mountain ambush.

The killing of the French troops did not sit well in France, and there likely will be renewed calls for a withdrawal of French troops, as there have been in some other European countries. Such popular discontent threatens to undermind NATO's military efforts in Afghanistan.

The other crisis is in eastern Europe and the Caucasus, where Vice President Dick Cheney just concluded a visit to show American support. The United States and some other European countries want Ukraine and Georgia to become members of NATO. Russia strongly objects to membership of its two neighbors and former satellites. In fact, analysts of the region say part of the reason for Russia's recent invasion of Georgia was prompted by its perceived threat of having NATO at its borders.

In some ways, the proposed NATO expansion poses a larger threat to the alliance than does Afghanistan. If Georgia had been a NATO member when Russian troops and tanks moved into the country, under Article Five of the alliance's charter, NATO troops would have been obligated to defend Georgia. If the alliance had not acted, it would have looked weak in the face of Russian military action. If it had attempted a military intervention, it might well have failed. Either way, there would have been disastrous consequences for the alliance.

Founded in 1949 to counter the Soviets during the Cold War, NATO still is a necessary alliance, promoting European and North American unity. With proper leadership from the United States, the Afghanistan mission can hold together and help defeat terrorists there. In Eastern Europe and the Caucasus, NATO must be very cautious about an expansion that it may not be politically or militarily able to support.

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