Eastern Europeans are rightly alarmed about the brazenness and success of the Russian blitzkrieg into Georgia. For many living in Russia's shadow, this is reviving traumatic memories -- of 1968 for Czechs, 1956 for Hungarians, 1939 for Poles. It does not help that senior Russian generals are threatening to rain nuclear annihilation on Ukraine and Poland if they refuse to toe the Kremlin's line.

Even those states which, unlike Georgia and Ukraine, are already in NATO can take scant comfort. As Poland's foreign minister, Radek Sikorski, says, "Parchments and treaties are all very well, but we have a history in Poland of fighting alone and being left to our own devices by our allies."

Warsaw's response has been to draw closer to the United States, by rapidly concluding an agreement in long drawn-out negotiations over the basing of U.S. interceptor missiles on Polish soil. That's a good start, but it's a move of symbolic import only. The small number of interceptors are designed to shoot down an equally small number of Iranian missiles -- not the overwhelming numbers that Russia deploys. Poland and other states should be under no illusion they can count on the U.S. in a crisis. In the past we left Poland, Hungary and Czechoslovakia in the lurch. More recently we haven't done much to help Georgia.

The only thing that the frontline states can count on is their own willingness to fight for independence. But willingness alone is not enough. They also need the means to fight, and at the moment they don't have them. We have already seen how the tiny Georgian armed forces -- with fewer than 30,000 men -- were routed by the Russian invaders.

What gets ignored is that Georgia, although a small country (population: 4.6 million), has the potential to do far more for its defense. According to the CIA's World Factbook, Georgia has over 900,000 men between the ages of 16 and 49. It could easily create a larger military force than it has, but that would require spending more on defense. By the CIA's estimate, its defense budget was just 0.59% of GDP in 2005.

Georgia's military spending has grown in recent years, but not Eastern Europe's. According to the International Institute of Strategic Studies, only one country in Eastern Europe spends more than 2% of GDP on defense. That would be Bulgaria at 2.2%. Romania is in second place at 1.9%, followed by Poland at 1.8%. Nor do these countries maintain large standing forces. Poland has 7.9 million males of military age but only 127,266 active-duty personnel in its armed forces. Hungary could mobilize 1.9 million men but has only 32,300 in uniform. Bulgaria has 1.3 million potential soldiers but only 40,747 actual soldiers. And so on.

There is one exception to this demilitarizing trend. Russia, which has more than a million soldiers under arms, has been increasing its defense budget from the lows of the immediate post-Soviet era. Based on official figures it spends at least 2.5% of GDP on its military. But if you add in expenditures on paramilitary forces and other items, the total comes closer to 4% -- roughly the same percentage that the U.S. is spending.

Small states have often shown the ability to humble great powers. In 1920, under the inspired leadership of Marshal Josef Pilsudski, the Poles staged a brilliant counterattack to save Warsaw and drive the Red Army off their soil. In the winter war of 1939-1940 the plucky Finns held off Soviet invaders, forcing the Kremlin to settle for a slice of its territory rather than all of it. More recently, the Afghan mujahedeen drove the Red Army out of their country altogether, thereby helping to bring down the Soviet Union.

But if they have any hope of emulating such feats -- or, more precisely, of deterring the Russians from threatening them in the first place by making it clear that they could emulate such feats -- today's Eastern Europeans have to do much more to prepare a robust defense. They should double their military spending to make themselves into porcupine states that even the Russian bear can't swallow.

The U.S. can help, as we helped the Afghans in the 1980s and as the French helped the Poles in 1920. That will require a readjustment in our military assistance strategy, which has been to create in Eastern Europe miniature copies of our own armed forces. Our hope, largely realized, has been that these states will help us in our own military commitments in Afghanistan, Iraq and elsewhere. But in addition to developing NATO-style expeditionary capacity, these states need to be able to conduct a defense in depth.

That means having large reserves ready for fast call-up and plenty of defensive weapons -- in particular portable missile systems such as the Stinger and Javelin capable of inflicting great damage on Russia's lumbering air and armor forces. That's more important than fielding their own tanks or fighter aircraft. We should offer to sell them these relatively inexpensive defensive systems, and to provide the advisory services to make the best use of them. But the first step has to be for the Eastern Europeans to make a larger commitment to their own defense.

Mr. Boot, a senior fellow at the Council on Foreign Relations, is the author, most recently, of "War Made New: Technology, Warfare, and the Course of History, 1500 to Today" (Gotham Books, 2006).

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