Greenland might not be for sale, but the ice-covered island is strategically crucial to American national security and will likely play an important role as the United States, Russia, and China compete in the Arctic.

President Trump has reportedly expressed interest in making an offer on the massive, self-governed region, which is part of the Kingdom of Denmark. The island has been crucial to U.S. homeland defense for decades and will likely increase in importance as the Pentagon refocuses on great power competition after years concentrating on counterterrorism.

"The U.S. [presence] that's currently in Greenland is absolutely vital to the defense of North America," Luke Coffey, director of the Heritage Foundation's Allison Center for Foreign Policy, told the Washington Examiner. "It provides the key early warning system for ballistic missile defense. So in that sense, it's a very important piece of real estate."

"However, it's not for sale," he added.

Greenland's foreign affairs ministry confirmed that Friday, saying that while the island is very interested in boosting trade and tourism, it's not interested in being bought outright.

"We're open for business, not for sale," the ministry said in a Twitter post.

[ Also read: Forget Greenland, focus on Puerto Rico and real issues, 2020 Democrats say]



#Greenland is rich in valuable resources such as minerals, the purest water and ice, fish stocks, seafood, renewable energy and is a new frontier for adventure tourism. We're open for business, not for sale❄️🗻🐳🦐🇬🇱 learn more about Greenland on: https://t.co/WulOi3beIC — Greenland MFA 🇬🇱 (@GreenlandMFA) August 16, 2019



Trump is not the first president to take an interest in Greenland. President Harry Truman sought to buy the island from Denmark for $100 million in 1946 at the dawn of the Cold War, though the Danes ultimately turned the offer down.

While the United States might not be able to buy Greenland, a longstanding treaty with Denmark gives the American military broad authority to operate out of Thule Air Base, the Pentagon's northernmost military installation. A crucial ballistic missile early warning radar system operates out of Thule, in addition to units from U.S. Air Force Space Command, the North American Aerospace Defense Command, and rotating Air National Guard units. The Coast Guard also maintains a regular presence in Greenland, sending ships to the region annually.

Greenland played a particularly important role in the Cold War, serving as a base of operations for over a dozen units starting in 1951. With Russia's return as a U.S. adversary, Greenland could once again serve as the front line for North American defense, especially since Thule is home to the northernmost deep-water port in the world.

"Thule Air Force Base in Greenland is a valuable surveillance and communications base, and its early warning mission has clear strategic importance," John Conger, director of the Center for Climate and Security, told the Washington Examiner. "It's also clear that as the Arctic ice melts and the permafrost thaws, dynamics in the Arctic will evolve, and there may be other important opportunities to leverage that strategic location."

Warmer temperatures have opened up Arctic sea lanes and mineral reserves previously unavailable for exploitation, and Russia has sought to stake a claim by building bases, ports, and sending an icebreaker fleet to the region. China has also declared itself a "near-Arctic state" in an effort to capitalize on the area's rich oil and gas reserves.

But it could be a while before Greenland's advantages become profitable.

"When you consider the additional costs and risks associated with using the northern sea route, it's not so clear that it's financially or economically viable," Coffey said. "But as the ice continues to melt ... maybe 100 years from now, this will become a very lucrative shipping route. But right now, it's not so much."

It could also take some time before Greenland's mineral deposits reap significant rewards because of the region's underdeveloped infrastructure. Of the 12 mining licenses the country has given out, Coffey said only two are in operation, and neither is profitable yet.

Washington's short-term defense interests in the Arctic, however, are very clear. In response to China and Russia, the Pentagon is relearning how to fight in the cold.

NATO forces held a military exercise called Trident Juncture last year in and near Norway with 50,000 participants, giving troops a taste of what Arctic combat might be like. The Marine Corps has also sent a rotating contingent of forces to Norway, where Marines are pre-positioning vehicles, weapons, and ammunition in massive caves and learning to fight on skis.

Noting the region's importance, Air Force Gen. Terrence O'Shaughnessy, head of U.S. Northern Command and North American Aerospace Defense Command, has said, "The Arctic is the first line of defense."