For nearly 20 years since the collapse of the Soviet Union and its Eastern European satellite system began in fall 1989, NATO planners did not have to contemplate the prospect of having to face any serious military challenges or conflicts in Europe. But in August, that changed.

The highly successful Russian invasion of the former Soviet republic of Georgia on Aug. 8, 2008, showed that the days of military conflict were not gone forever in Europe. The Russian army's blitzkrieg offensive took the U.S. government and the planners of the North Atlantic Treaty Organization by surprise. Georgia was not a NATO member, although the Bush administration in Washington had wanted it to become one. Still, the United States had lavishly supplied Georgia with helicopters, anti-aircraft missile systems and a wide range of weapons and equipment. Virtually all of them fell unused into the hands of the Russian army after less than five days of combat operations.

Russian leaders later expressed displeasure at aspects of their armed forces' performance. They felt that their aircraft were unexpectedly vulnerable to U.S.-supplied anti-aircraft missile systems -- about the only equipment supplied to the Georgians that they operated well. And Russian generals were concerned that command and control of their forces was poor. Major programs were later announced to address these deficiencies.

But judged by any conventional standards, the Russian military performance was impressive, and it contrasted dramatically with the long, bloody years of military operations in Chechnya, elsewhere in the Caucasus, from 1999 well into the 21st century.

The lesson for planners and policymakers of the U.S.-led North Atlantic Treaty Organization should have been clear: Major land wars that could involve U.S. armed forces against formidable opponents were no longer inconceivable.

Later that fall, as NATO belatedly organized a show of support for embattled Georgian President Mikheil Saakashvili, retired Adm. Eduard Baltin of the Russian navy issued a grim warning. He publicly stated that the Russian Black Sea Fleet and its land-based air-support assets could sink all U.S. and NATO warships operating in the Black Sea within 20 minutes.

Baltin's warning of course did not mean that a shooting war between the Russian armed forces and NATO warships operating in the Black Sea was inevitable or imminent. But it did signal that to planners in Moscow, such a conflict was no longer inconceivable. For that matter, the Black Sea is a body of water that has been under Russian control or domination except for brief periods of time throughout the past 250 years.

The lessons of what happened in Georgia fly in the face of the conventional wisdom complacently assumed by U.S. and NATO military planners since the collapse of communism. They have embraced the idea that gigantic, full-scale land wars on major continents involving hundreds of thousands or even millions of troops had become inconceivable.

That is also the wisdom in every major nation of the European Union, and it's especially the case among European Commission policymakers in Brussels.

The only trouble is that Russian policymakers do not believe it is true -- and are planning based on very different assumptions.

Part 6: Russia's 21st century challenge to NATO