President Trump on Thursday was expected to visit the Al Udeid Air Base in Qatar, the largest U.S. military facility in the Middle East and considered “essential to regional security” by the Pentagon.

The U.S. military has been using the base since September 2001, when it positioned planes there to target the Taliban and Al Qaeda in Afghanistan. Two years later, Al Udeid became the main U.S. air operations hub in the region.

U.S. commanders used Al Udeid to coordinate a wide variety of missions during the wars in Iraq and Afghanistan, as well as strikes against ISIS in Syria. The air force has deployed a wide variety of aircraft, from advanced fighters and long-range bombers to drones, transport planes and in-flight refueling tankers.

The Combined Air Operations Center at the base helps project U.S. air power across a vast region encompassing 21 countries, from Northeast Africa to Central and South Asia, according to the U.S. Air Force.

Qatar, which saw the United States as its main protector in the Middle East, finished building the base in 1996, hoping to encourage the deployment of the U.S. military there.

Over the years, Qatar has spent more than $8 billion to develop the base, which its military also uses alongside the British Royal Air Force, as part of Qatar’s efforts to build up its partnership with the United States. The statement of defense cooperation signed between Qatar and the United States on Wednesday included $38 billion in potential investments, including support for burden-sharing at the base.

In a nod to the partnership, Qatari and American flags flanked the stage set up for Mr. Trump at Al Udeid on Thursday. An American Reaper drone was displayed on one side of the stage, and a Qatari F-15 fighter jet on the other.

The modernization and expansion of the base has allowed a number of key U.S. military commands to operate out of Al Udeid. Along with the U.S. Central Command, the base also hosts command facilities for special forces.

The base has played a role outside of offensive military operations too. In 2021, as the U.S. military withdrew from Afghanistan, Al Udeid became the central evacuation point for tens of thousands of people leaving Afghanistan, including Americans and Afghans considered at risk from the Taliban.