LONDON -- America's notion of its national sense of "manifest destiny" has been a mainstay of its internal expansion and then its involvement with the world in the past century. This has frequently been of enormous benefit to the rest of the globe. But it can lead the most powerful nation on Earth into undertakings that would be best tempered with a less visionary approach.

The doctrine of manifest destiny was initially enunciated to justify the expansion from the east of the North American continent to occupy the whole of the land mass to the Pacific Ocean. In the last century, it took on a wider meaning as the United States became a superpower, and engaged with the rest of the world.

In World War II, the might of U.S. arms was accompanied by a conviction that the spread of democracy made the conflict a struggle between good and evil. Then there was a manifest destiny in America's backing for the defense of the West in the Cold War with the Soviet Union. More recently, it merged with the economic spread of globalization to bring a Clinton-era conviction that the planet could be made a more unified, less fractious place by enlightened internationalism, spearheaded by the U.S. with the help of free markets.