The North Atlantic Treaty Organization is marking its fiftieth anniversary this month and next by adding Poland, the Czech Republic, and Hungary into the fold. This historic move into Eastern Europe is altering more than NATO’s membership roster. In these new members, we catch a glimpse of NATO’s new mission.

When NATO’s founding fathers convened in Washington to create the alliance in 1949, their goals were simple but sweeping: safeguard freedom, preserve the peace, and encourage economic collaboration through a system of collective defense that bound the strongest member to the weakest.

NATO’s founding members had good reason to close ranks. By the end of 1945, Soviet leader Josef Stalin had already broken the promises he made at Yalta to hold free and open elections in Eastern Europe, which by that time was occupied by the Red Army. As Stalin consolidated the spoils of war, Churchill concluded in 1946 that an "iron curtain" had descended on Europe, dividing a free West from an imprisoned East.

A year later, Moscow began to destabilize Western Europe’s war-weary governments by staging riots, deploying spies, and even fomenting civil war in Turkey and Greece. Tensions came to a head in 1948, when the Soviets orchestrated a coup in Czechoslovakia and blockaded Berlin, thereby violating the Potsdam agreements.

Ten months later, NATO was formed. Nearly a half-century would pass before we heard again from those trapped behind Stalin’s iron curtain.

For most of this century, NATO bolstered the West; now, it prepares to stabilize the East. Today, NATO’s members finally step across the artificial division lines of Europe and welcome Poles, Czechs, and Hungarians as equals in the greatest war-preventing alliance in history.

Stabilizing Europe is really not a new idea for the Alliance. In fact, the North Atlantic Treaty openly sought to "promote stability throughout the North Atlantic area." As this area expands, so too has NATO’s ability to stabilize the continent that spawned two world wars.

We’ve learned in the last decade that the Alliance will intervene in Eastern Europe’s crises only as a last resort, but that may have to change. Brokering peace and defusing wars will be key to the success or failure of NATO’s new mission. In Bosnia and Kosovo and a dozen other ethnic flashpoints, that mission must be to project stability. (This mission will be severely hampered if the United States and its NATO allies continue to issue empty threats to dictators like Slobodan Milosevic.)

Make no mistake, there will be no peace without stability, and Eastern Europe is anything but stable without NATO. It was not the European Union or United Nations that pacified Bosnia—it was NATO. Only after the United States led NATO into the Balkans did the bloodshed end. While NATO has not brought real peace to Bosnia, it has provided that essential ingredient to peace—stability. It appears the Alliance is primed to do the same in Kosovo.

By setting-up shop in Eastern Europe, NATO may even be able to preempt the next round of Yugoslav-style ethnic wars. There are plenty of simmering disputes in Eastern Europe: Bosnia, Croatia, and Serbia will plunge back into war should NATO withdraw; Moldova and Georgia are under tenuous cease-fires; Ukraine is divided between a pro-Russian eastern half and a nationalist western half; the Baltics have raised Moscow’s ire by mistreating ethnic Russians; and Russia itself is comprised of no less than 100 unique ethnic groups.

Despite these challenges, NATO clearly remains a potent and positive force throughout Europe. It’s worth noting that Slovenia, the only part of the former Yugoslavia bordering a NATO member, was able to break free from Milosevic in a matter days, with little bloodshed.

In fact, the mere possibility of NATO membership has prompted Romania to settle territorial and ethnic disputes with Ukraine. The same is true for Albania and its improved treatment of Greek minorities. As a precondition of joining NATO, Hungary had to iron out long-standing problems with Romania, as did Poland and Lithuania.

NATO’s new mission won’t replace the old. The Alliance still faces Moscow, and for good reason. While Russia is not the same as the Soviet Union, nor has it been fully reformed. The Russian parliament, while politically weak, is dominated by communists and ultra-nationalists who want to reverse the outcomes of the Cold War. Their power is checked by a constitution that grants the president near-dictatorial authority, but their growing numbers give us a picture of what Russian voters believe: Many Russians view America not as a partner, but as a source of humiliation and defeat.

Their discontent is well-founded: The ruble is worthless; international investors are packing up; the GDP fell by 10% last year; the unemployment rate is six times higher than that of the United States. The Red Army, once a symbol of strength and pride, is a collection of underpaid gangs, its global empire gone.

Boris Yeltsin, Russia’s Western-oriented president, is ailing. Given the current political and economic conditions, it is unlikely that his successor will be as friendly and responsible as the man who pulled the plug on the Soviet Union.

Any or all of these factors could contribute to the collapse of the status quo and the revival of Cold War. NATO must be ready for that grim possibility.

Just as the NATO we leave behind protected the West, the new NATO must project stability eastward. If we entertain any hopes of preventing another Bosnia, or of winning another Cold War with Moscow, a strong and pro-active NATO is essential. But that, of course, depends on a strong and pro-active America at NATO’s helm.