In my latest documentary, we describe Russian President Vladimir Putin as the most powerful man in the world. But why? After all, the United States -- and China, for that matter -- are more powerful countries than Russia.

The power of a head of state is determined both by the country's strength and the capacity he or she has to exercise that power, unilaterally, unconstrained by other institutions, parties and political forces. And combining those two metrics, it's easy to see why Vladimir Putin rises to the top of list.

Putin has created what he calls a "vertical of power," something unlike any we see in other great nations. As the Russian chess grandmaster Gary Kasparov -- himself a harsh critic of Putin -- has noted, the entire structure of Russian political power rests on one man. When the czar died, you knew the structure that would endure and the process by which his successor, his son, would be elevated. When the general secretary of the Soviet Communist Party died, the Standing Committee and the Politburo would select his successor. But when Putin dies -- I almost wrote if -- what will happen? No one knows.

To understand Putin, you have to understand Russia. The last hundred years for that country have seen the fall of the monarchy, the collapse of democracy, the great depression, World War II with its tens of millions of Russians dead, Stalin's totalitarian brutalities, the collapse of communism, the breakup of the Soviet Union, and Boris Yeltsin's years of chaos and corruption.

Then comes Vladimir Putin, who ushers in stability and, in popular perception, rising standards of living and increasing prominence and respect in the world. That respect is important.

Russians have immense national pride. Russia is the largest country on the planet -- 48 times larger than Germany and encompassing 11 time zones that straddle Europe, Asia, and the Middle East.

Russia is also a rich country, containing some of the largest deposits of raw materials, from oil and natural gas to nickel and aluminum. Culturally, it has often thought of itself as the third Rome, preserving Christianity even as Rome and Byzantium fell to the Barbarians.

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