The World's Most Dangerous Theory

Interesting point in yesterday's entertaining Tony Blair speech:

There is no more dangerous theory in international politics today than that we need to balance the power of America with other competitor powers, different poles around which nations gather. Such a theory may have made sense in 19th century Europe. It was perforce the position in the Cold War. Today, it is an anachronism, to be discarded like traditional theories of security.

Italics mine. Speaking theoretically for a moment, does that seem logical? That the removal of competition, and the emergence of a single dominant military power, is the best way to go? I'd always guessed that competition was a good thing, that power tended to corrupt, and that people without it were incentivized to behave irresponsibly. But maybe that's just a dangerous theory.