America's announcement this week that it will end its military presence in Saudi Arabia is part of what will likely be the biggest change in where American troops are deployed since the height of the cold war.
The Iraq war has encouraged a shift toward a newer set of allies - from Bulgaria to Qatar - as the forward outposts of US power.
Longer term, America's military is seeking the ability to deploy large forces without reliance on allies' ports and airbases.
The shift comes in the wake of a war that eliminated the Middle East regime of greatest concern to the US but also highlighted how vulnerable America is to being denied toeholds by reluctant allies.
Turkey limited access for US forces, costing America the use of a quarter of its invasion force to open a northern front in Iraq. Air-base limits by Saudi Arabia forced the Pentagon to scramble for ramp space at bases throughout the Persian Gulf.
"The US cannot go out and beat up on someone unilaterally if we do not have diplomatic arrangements with someone in the local area who can provide access," says retired Army Lt. Gen. Charles Otstott.
Some of the redeployments being announced were prompted by victory in Iraq. The demise of Saddam Hussein's regime means dozens of planes are no longer needed at bases in Saudi Arabia and Turkey to enforce no-fly zones in Iraq. Already, US warplanes based at Incirlik Air Base in Turkey quietly departed for the US and the command center for US air operations will soon shift from Saudi Arabia's Prince Sultan Air Base to Qatar.
Instead, US forces will be stationed and train in Bulgaria, Hungary, Romania, former Soviet Republics such as Uzbekistan, and Qatar, where they can have unencumbered access to Afghanistan and Iraq or other nations of strategic concern. As part of the war against terror, US forces are operating in large numbers in East Africa for the first time.
The shift toward these allies stems in part from political factors. In Saudi Arabia, the US departs a country where its decade-long presence has fostered anger and been the target of terror attacks. A truck bombing of the Khobar Tower military barracks in Dhahran, Saudi Arabia, killed 19 airmen in 1996. Osama bin Laden made ending the US presence in that nation, home to Islam's holy city of Mecca, a prime goal of Al Qaeda.
In Western Europe, congestion and environmental concerns make training exercises difficult. "You can do more realistic training because the rules about using ranges are less strict in Romania or Bulgaria," says former Assistant Defense Secretary Ashton Carter.
Given the hostility and fickle allies encountered abroad, the US military would prefer to eliminate its dependence on foreign bases altogether in the distant future. Future enemies and even allies who oppose US military intervention might learn from the Iraq war that the best way to thwart the overwhelming American military advantage on the battlefield is denying access to bases near the target, says a senior government defense analyst. "You don't want to give the US a toehold," says the defense analyst. "Give us a toehold and you have big trouble on your doorstep."
Instead of massing large numbers of forces in Europe and Asia - each of which still host 100,000 American service members - the US may rely more on warehoused prepositioned equipment that can be matched up near a trouble spot with more mobile units based in the continental US.
Already, the US prepositions equipment for whole brigades of troops on the Indian Ocean island of Diego Garcia as well as US territories in the Pacific such as Guam. Ships from those bases must now dock at ports to unload, but military planners are exploring how to transfer the equipment directly to landing craft that could operate without docking.
"The US does not need local bases in order to project power effectively," says Mr. Carter, now at Harvard University's Kennedy School of Government
A model future base is Whiteman Air Force base. Landlocked in rural Missouri, the base can project power to any point in the globe within 24 hours. Whiteman's B-2 bombers can fly anywhere on earth nonstop, launching 30-hour missions to Iraq or Afghanistan and coming home for dinner with their families.
Similarly, the Marine Corps is eyeing a future when it won't depend on foreign bases. During the war in Afghanistan, most of the operational support and intelligence received by troops on the ground came from Quantico, Va., says Marine Corps Commandant Gen. James Jones.
Marines could have a "lesser footprint" on the ground by relying more on Navy ships to house command-and-control or to do the maintenance on Marine trucks, says Noel Williams of the Marines' Center for Emerging Threats and Opportunities.