WASHINGTON—In “Rebuilding Russia,” published as the Soviet Union was on the verge of collapse, Alexander Solzhenitsyn wrote that the “awakening Russian national self-awareness has to a large extent been unable to free itself of great-power thinking and of imperial delusions ... it has taken over from the communists the fraudulent and contrived notion of Soviet patriotism.” As all prescient statements, it was a shrewd reading of the present, not the future. The Russian invasion of Georgia is a powerful confirmation of Solzhenitsyn’s words.

Of course, one could reverse his argument: Soviet imperialism was a continuation, not an antecedent, of Russian nationalism. Vladimir Putin and his stooge, President Dmitry Medvedev, have revived a tradition of Russian expansionism that dates back to Ivan the Terrible. The invasion of Georgia echoes Russia’s annexation of that country in 1801 and again in 1921, when the Soviets crushed a short-lived Georgian independence.

This has little to do with protecting South Ossetians, who a few years ago were vying for independence from both Georgia and Russia. And it has little to do with Georgian President Mikheil Saakashvili’s obvious miscalculation in responding to South Ossetia’s latest provocation by trying to assert military control of that region. Russia had been planning this for some time, as demonstrated by the awesome efficacy of the assault, targeting areas well beyond South Ossetia and Abkhazia, another rebellious region, and mobilizing its Black Sea fleet.

It would also be a gross mistake to think that the casus belli can be traced to Western actions such as the recognition of Kosovo’s independence to the detriment of Russia’s Serbian allies or NATO’s push for an anti-missile system in Central Europe. Those moves, however imprudent given the psychology of Moscow’s leaders, did not precede the emergence of post-Soviet nationalism in Russia. Quite the opposite: Moscow’s foreign expansion is the logical continuation of authoritarian rule at home, which Putin has been consolidating for some time with the help of abundant oil and natural gas money.

First, Putin made sure his country’s feeble democratic institutions were replaced with autocratic rule. Most checks and balances were neutered: the judiciary, political parties, local governments, the media, private corporations, separatist regions. The security forces, the Orthodox Church and the energy industry became the pillars of the new regime. The first two, already steeped in Russian nationalism, required little purging. The energy sector needed some work, which is why the giant Yukos firm was broken up and its oil subsidiary gobbled by the government, as was Gazprom, the world’s largest producer of natural gas.

Once the Kremlin’s control was established, there was little anyone could do about Russian expansionism. Europe imports vast amounts of natural gas and oil from Russia. The threat to reduce or cut off supplies, for instance by ceasing shipments through Ukraine, a major transit route, served to blackmail the European Union.

Russia would like to get its hands on everything that lies between the Baltic and the Caucasus (beyond that, its big southern neighbor, Kazakhstan, ruled by a tyrant sitting on oil, is already a friend of Moscow’s). But there are some hurdles, including the fact that the Baltic and most of the Balkans are part of the European Union and NATO. Which leaves Georgia and Ukraine, whose revolutions in 2003 and 2004 were seen as a powerful assertion of Western values in a region that Russia considers its backyard, as the easiest targets.

Russian nationalists, who are impetuous but not crazy, know well that Central Europe is beyond their reach, but they could seriously undermine those nations if they controlled their next-door neighbor, Ukraine. And Georgia would give them control of the transit route between the Caspian Sea and the Black Sea, which is to say the Mediterranean.

What we have seen in Georgia these past few days is nothing less than the perfectly rational decision by Russia to take that country’s born again nationalism one step forward. It is important to understand this reality now that the debate about whether to isolate, engage or ignore Russia is about to begin in earnest in the West.

In 1990, Solzhenitsyn, who was himself a Russian nationalist of sorts, wrote that “it must be declared loudly ... that ... Transcaucasia ... will be separated off unequivocally and irreversibly” from Russia. I wonder what he would think of his friend Putin’s decision to prove him wrong.