US deployments across Mideast factor in Iran tensions US military deployments across Mideast, rooted in 1991 Gulf War, now a factor in Iran tensions

DUBAI, United Arab Emirates -- A U.S. aircraft carrier strike group rushes toward the Persian Gulf. Decades-old B-52 bombers rumble down runways at desert air bases. The Pentagon, meanwhile, routes a Patriot missile battery and an amphibious supply ship to return to the region.

These military deployments in the Persian Gulf, beginning with a sudden May 5 order from the White House citing still-unspecified threats from Iran, comes as Tehran has begun setting its own deadlines over its unraveling nuclear deal that President Donald Trump pulled America of out of a year ago.

Yet even without these movements, the U.S. has maintained a vast network of bases across the Persian Gulf dating back to the 1991 Gulf War against Iraq. Allied Gulf Arab nations, many rich from oil reserves, equip their own forces with billions of dollars of American arms as well.

Here's what military assets the U.S. has across the Persian Gulf, those it is now bringing in, and why America has maintained its long presence in the region.

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'UNRELENTING FORCE'

John Bolton, Trump's national security adviser, announced the deployment of the USS Abraham Lincoln aircraft carrier and its strike group on May 5 over "troubling and escalatory indications and warnings" that still have not been specified. He warned Iran any attack would U.S. interests or allies would face "unrelenting force." The Lincoln, which left the U.S. in April on a scheduled deployment, had planned to come to the Persian Gulf on its around-the-world trip to San Diego, California. Now it is steaming there earlier. Alongside the Lincoln are three destroyers, the USS Bainbridge, the USS Mason and the USS Nitze, as well as the guided-missile cruiser the USS Leyte Gulf and a Spanish frigate, the ESPS Mendez Nunez.

Separately, B-52s from the 20th Bomb Squadron of Barksdale Air Force Base in Louisiana have landed in Qatar and elsewhere in "southwest Asia" — possibly the United Arab Emirates — in recent days.

On Friday, the Pentagon announced it would be returning a Patriot missile battery to the wider Mideast, as well as sending the USS Arlington, an amphibious warship carrying U.S. Marines. The USS Kearsarge, an amphibious assault ship carrying Marines and warplanes, just left the Persian Gulf and is nearby in the Arabian Sea.

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U.S. BASES, PERSONNEL IN THE REGION

The Persian Gulf hosts a series of major American military installations.

The U.S. Navy's 5th Fleet, which oversees the region, is based in Bahrain, an island nation off the coast of Saudi Arabia that is home to over 7,000 American troops. Kuwait hosts over 13,000 American troops and the U.S. Army's Central forward headquarters. Dubai in the United Arab Emirates is the largest port of call for the U.S. Navy outside of America. The UAE hosts 5,000 U.S. military personnel, many at Abu Dhabi's Al Dhafra Air Base, where American drones and advanced F-35 jetfighters are stationed. The forward headquarters of the U.S. military's Central Command is at Qatar's sprawling Al Udeid Air Base, home to some 10,000 American troops. In Oman, the sultanate allows thousands of overflights and hundreds of landings a year, while also granting access to ports and its bases.

Meanwhile, U.S. special forces personnel reportedly are on the ground in Yemen amid the Saudi-led war against the Houthi rebels. The U.S. also carries out a yearslong drone-strike campaign there targeting suspected members of al-Qaida in the Arabian Peninsula.

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U.S. PRESENCE FROM THE CARTER DOCTRINE TO THE WAR YEARS

During the Cold War, the U.S. pledged to defend its Persian Gulf allies from the Soviet Union. By the start of 1980, however, the region was in turmoil.

The Islamic Revolution in Iran had thrown out the American-allied shah. The Soviet invasion of Afghanistan sparked fear in the administration of President Jimmy Carter that Moscow could be within striking distance of the Strait of Hormuz, the narrow mouth of the Persian Gulf through which a third of all oil traded by sea now passes. The president's eponymous Carter Doctrine emerged from that. It holds that the U.S. would use military force to defend its interests across the energy-rich Persian Gulf.

But what would cement the U.S. presence in the region came in 1990, when Iraqi dictator Saddam Hussein invaded his oil-rich neighbor Kuwait. Defense agreements struck with Gulf Arab nations then grew into a series of major military installations across the region. The presence of American troops in Saudi Arabia, home to the Muslim world's holiest sites, served as a chief complaint of al-Qaida leader Osama bin Laden ahead of the Sept. 11, 2001, attacks. Those attacks led to the U.S. war in Afghanistan, which continues today over 17 years later.

The 2003 invasion of Iraq and the chaos that followed, including the rise of the Islamic State group there and in Syria, only increased the importance the U.S. holds on its bases in the region.

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THE VIEW FROM IRAN

Iran's Shiite theocracy long has looked at the presence of U.S. forces ringing its country with suspicion. One flash point is the Strait of Hormuz in the territorial waters of Iran and Oman, which at its narrowest point is just 33 kilometers (21 miles) wide. The width of the shipping lane in either direction is only 3 kilometers (2 miles).

The strait is viewed as an international transit route. American forces routinely travel through the area, despite sometimes-tense encounters with Iran's Revolutionary Guard, a paramilitary force answerable only to Supreme Leader Ayatollah Ali Khamenei. For its part, Iran compares the American presence to Tehran sending warships to the Gulf of Mexico.

"Breaking: Our Navy operates in - yes, correct - the Persian Gulf, not the Gulf of Mexico. Question is what US Navy doing 7,500 miles from home,"

Iranian Foreign Minister Mohammad Javad Zarif once tweeted in 2017, attaching a map showing the distance between the two bodies of water.

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Follow Jon Gambrell on Twitter at www.twitter.com/jongambrellAP.