Although US forces deployed to the Persian Gulf are smaller in absolute size than they were in 1991 for Operation Desert Storm, America is sending a higher proportion of its combat units into battle at once than it has in decades.
Analysts say the US still has the capability - through air power - to respond to possible flashpoints such as Korea or Taiwan.
But, despite a longstanding military doctrine of "two-war" capability, a long war or occupation of Iraq will strain the military's ability to do much more than hold out against other potential enemies.
"It's a substantial portion of the force structure [in the Gulf], and it's not something that could be sustained," says Owen Cote, associate director of the Massachusetts Institute of Technology's security studies program.
The US has committed most of its heavy ground forces and deployable aircraft carriers, as well as a large share of its best attack aircraft and air- and sea-lift units.
Five carrier battle groups are already in the Gulf region and a sixth is on the way, leaving only a couple of the Navy's 11 carrier air wings left to for possible deployment, since some are now in dock for maintenance or overhauls.
The military has now ordered at least five of its 10 active Army divisions and one of three Marine divisions deployed to the Gulf. Those include America's most mobile parachute- and helicopter-borne divisions, and some advanced mechanized forces.
This massive deployment comes as US military strategy has evolved away from a strict "two-war" strategy. The new standard: being able to fight overlapping - but not necessarily simultaneous - conflicts. The 2001 Quadrennial Defense Review called for US forces "decisively defeating" an adversary in one theater, including the ability to occupy territory or change a regime.
This approach, known as "win-hold-win" supplanted a two-war approach that assumed the regional conflicts in Iraq and Korea. "You fight in one region, hold in one region and then go in and finish the fight in the [second] region," says retired Maj. Gen. Robert Scales, the former head of the Army War College.
Perhaps most the most significant Gulf-related strain on US capabilities is on air- and sealift capacity. The Pentagon invested billions during the 1990s in fast new "roll on/roll off" cargo ships capable of quickly transporting the Army's heaviest units. But about 45 of those 50 ships, owned by the military and manned by civilian merchant mariners, are either delivering materials to the Middle East or on their way back, says Cote.
The sealift crunch has forced the military to postpone indefinitely deployment of one armored division slated for Iraq, Stars and Stripes newspaper has reported.
For only the second time ever, the US has activated the Civilian Reserve Aircraft Fleet, which gives the military access to civilian jumbo jets. So far, the Pentagon has activated only a few dozen passenger jets to move troops to the Gulf.
America would respond to a crisis involving South Korea or Taiwan by deploying large numbers of warplanes that could help those countries hold off attackers until US ground forces could be redeployed for a counteroffensive, analysts say.
In the unlikely event of a Chinese attack on Taiwan, the US would respond by deploying several hundred air-to-air fighters to bases on the island or Okinawa.
Korea appears more volatile for now. South Korea maintains a potent ground force, while the North's military has weakened in recent years. American warplanes armed with precision-guided munitions could help hold out against any conventional attack. "We do have the capability to handle a Korea," says retired Adm. Jonathan Howe.
As a show of force against North Korea, the US has recently deployed B-52 and B-1 bombers to Guam and F-117 stealth fighters to South Korea. The USS Constellation carrier group is also nearby. But Mr. Scales says the Pentagon would find it hard to implement existing Korean war plans, which call for armored divisions to be shipped from the US.
But even if the US hadn't committed such a large force to the Gulf, little in the American arsenal could do much to protect South Korea from the North's most potent weapons: chemical weapons and artillery tubes within range of Seoul.