Yet today the US global military presence is perhaps more pervasive than ever before.

In part this is due to the war on terrorism. US units are settling into new bases in and around Afghanistan on a semi-permanent basis. Hundreds of other US soldiers will soon arrive in the Philippines to help fight local terrorists linked to Al Qaeda.

But it also stems from the fact that a generation of Washington policymakers has come to see the US as an indispensable force in many troubled regions. Thus Camp Bondsteel, in Kosovo, today still houses thousands of US troops. Ten years after the Gulf War, US bases still dot Southwest Asia.

"It makes me nervous that, like the British, we've acquired an empire in a fit of absent-mindedness," says John Pike, a national security expert at GlobalSecurity.org. The key aspects of today's US military deployments, according to Pike, are their scope, and their durability.

During World War II, the US shipped many more uniformed personnel around the world than it has today. But that was clearly a temporary situation. The vast majority came home when Japan and Germany were defeated.

During the Cold War, the US deployed large numbers of troops on open-ended missions to contain communism. But most were concentrated in western Europe. Many of those bases were shut since the fall of the Berlin Wall.

In 2002, US forces are spread from Kosovo to Kuwait to Korea. In many of these places, they are permanently integrated into the local security structure.

"They're not just a bunch of guys passing through," says Pike.

Take the case of Afghanistan. US forces in the region will surely be reduced in months ahead as the last remnants of the Taliban are rounded up. But the military is unlikely to leave altogether. The Pentagon is creating an infrastructure of bases and political agreements that could lead to a US presence in the region that lasts years.

One key installation is the Manas airfield, near Bishkek, the capital of the former Soviet republic of Kyrgyzstan. US engineers are transforming it into a transportation hub capable of housing and handling thousands of troops -- yet it is only 200 miles from China.

The US is pouring concrete for runways, installing communications equipment and rough housing, or doing some other sort of improvement work at some 13 locations in nine countries in the central Asian region, including Uzbekistan and Pakistan.

Asked on January 14 whether the US now anticipates a long-term military presence, or increased military engagement, in the area, Deputy Secretary of Defense Paul Wolfowitz said "for sure".

The US already views its relationship with Uzbekistan and Pakistan differently than it did before September 11, said Wolfowitz, for both the short and long term.

It's not clear whether the US will have to deal with a continuing military threat in Afghanistan. But beyond that, commanders want to be able to return quickly if trouble develops again. The US wants the region's nations to know that it is still interested in their welfare.

"We're not just going to forget about them now that we've found them very useful," said Wolfowitz.

Similar calculations have led to the continued US presence in Kosovo and the Gulf, say other experts. It's easy to say the US shouldn't be the world's policeman -- and many politicians and officials have. But to withdraw, once engaged, is to risk irrelevance.

If the US were to reduce its military footprint in the Gulf, for instance, it might lose influence over the world oil market, find it harder to defend Israel, and become less important to the Middle East peace process.

"We shouldn't kid ourselves that we can exercise global influence on the cheap," says Stephen M. Walt, a professor of international affairs at Harvard's John F. Kennedy School of Government.

That does not mean all US commitments are unassailable, adds Walt.

Indeed, some have argued that the lesson of September 11, in part, is that the US needs to reduce its global presence. Al Qaeda terrorist attacks were a violent reaction to American preeminence, they say.

In an article in the current issue of The Atlantic Monthly, Benjamin Schwarz and Christopher Layne propose a new grand strategy for the US which involves passing the buck for enforcing security in troubled regions to Europe, Japan, and other US allies.

The strategic point of many US deployments is both to enforce order and prevent other nations, including US friends, from becoming strong enough to do so. [ Jacq' says, “What?” ]

Yet "the adult supervision, of the world is an enormously expensive and complex undertaking," write Schwarz and Layne.