President Donald Trump has reportedly expressed strong interest in buying the island of Greenland from Denmark for its resources and geopolitical significance.

Trump repeatedly asked his advisers with 'varying degrees of seriousness' if it would be possible for the U.S. to acquire the autonomous Danish territory, two sources told the Wall Street Journal.

'What do you guys think about that?' Trump asked a table of aides about the island purchase last spring, a source said. 'Do you think it would work?'

It's unclear how exactly the U.S. would go about buying the largest island in the world after failed American attempts to purchase Greenland in 1867 and 1946.

Greenland's government has insisted that it is not for sale, though the government of Denmark, which oversees the territory, has yet to comment. Trump is set to visit Denmark next month.

President Trump is showing strong interest in buying the island of Greenland as sources reveal he has repeatedly asked his advisers if it would be possible

The 811,000-square-mile island of icy terrain in the Atlantic inhabits about 56,000 people and is an autonomous Danish territory

Why would US want to purchase Greenland? Greenland is 811,000-square-miles - roughly the size of Western Europe and the largest island in the world. The Danish autonomous territory is located between the North Atlantic and Arctic oceans, and has significant natural resources and geopolitical significance. The US already maintains an airbase there - Thule Air Base, which is America's northernmost base. During the Cold War, Thule was a critical facility due to its location across the pole from the USSR. The base's secret construction, undertaken by an armada of 120 ships, has been compared in scale to the effort required to build the Panama Canal. Greenland is believed by some geologists to have some of the world’s largest remaining oil resources. China, perhaps eyeing these resources, has attempted to establish an economic foothold by financing three airports. Last year the Pentagon managed to block China's efforts. Advertisement

The 811,000-square-mile island of icy terrain in the Atlantic inhabits about 56,000 people, and though it is technically in North American waters, the self-governing land is culturally European.

Its foreign and security policy is handled by Copenhagen.

During last spring's exchange with advisers, Trump reportedly got the idea after hearing that Denmark was having financial problems because of the subsidies it pays to Greenland.

According to the Journal, Greenland relies on $591 million of subsidies from Denmark annually, which make up about 60% of its annual budget.

The U.S. already has an airbase in Greenland, which is part of a state-of-the-art ballistic missile early warning system and satellite tracking system.

It has also, in the past sought to derail China's efforts to make its mark on the independent territory.

In 2018, the Pentagon, alarmed at the news China was looking to finance the building of three airports on the ice-covered land, managed to block the move.

The US, along with its allies offered alternative funding options to Greenland in an effort to dissuade it from an expensive deal with China.

The 811,000-square-mile island of icy terrain in the Atlantic inhabits about 56,000 people, and though it is technically in North American waters, the self-governing land is culturally European

Icebergs are photographed from the window of an airplane carrying NASA Scientists as they fly on a mission to track melting ice in eastern Greenland on Wednesday

Concerns were centered around whether the aid-dependent government could afford a large loan from China, and if it failed in its efforts to repay it, could lead to China taking control of the runways, bringing in warplanes, creating new shipping lanes and gaining access to a wealth of resources in the Arctic.

This would undoubtedly post concerns in a nation, such as the United States, which as is frequently noted, is concerned with maintaining its global influence and military and territorial might - in particular against the two other great military powers, China and Russia.

As the Foreign Policy journal writes, 'Russia and especially China are the only two countries that could plausibly take over and hold the territory of Washington’s allies and partners in the face of US resistance'.

If either of the other two global powers ever gained the upper hand, it could see the balance of power shift. Such a shift could see China gain greater control over the economically dynamic area of the Western Pacific and could open Eastern Europe up to Russian control.

There are a number of reasons the territory could be proving attractive to the US President, including giving him a legacy that echoes that Thomas Jefferson earned in part through the completion of the Louisiana Purchase in 1803.

Greenland's vast natural resources

The island's natural resources, spread across 811,000 square miles, could also be one of the key attractions for the president.

As the climate changes and the arctic caps melt, there has been widespread interest in what is thought to be a rich potential of mineral and energy resources - iron ore, lead, zinc, diamonds, gold, rare-earth elements, uranium and oil.

A report in 2014 showed this map of areas of hydrocarbon development in Greenland. Hydrocarbon exploration is the search by geologists for deposits of substances such as petroleum and natural gas in the Earth

Research shows Greenland has been melting faster in the last decade and this summer, it has seen two of the biggest melts on record since 2012.

Both warmer air and warmer water are eating away at Greenland, causing it to lose billions of tons of ice daily in the summer.

And while a team of scientists and engineers are only just dropping probes into the ice to help figure out which is the bigger cause, water or air, one thing is certain, less ice could make the ability to uncover sub-earth treasures more feasible.

With less ice, access to this rich pool of resource beneath the land could become easier - making Greenland a territorial interest for the global powers.

A 2014 report, titled: The Greenland Gold Rush: highlighted how climate change had made waters around the icy territory more accessible.

'Only in recent years have exploration activities resumed as a result of global warming opening up parts of the Arctic, including areas in Greenland, along with dramatic increases in raw material demand and mineral prices in the mid-2000s.

It found within Greenland, the self-governing body is looking at a way of using these natural resources to help it rely less on foreign-aid and investment and become more economically and politically independent from Denmark.

Trump is scheduled to make his first visit to Denmark early next month, although the visit appears to be unrelated to any real desire to purchase Greenland.

The secretary of state, Mike Pompeo was also supposed to visit Greenland earlier in the year to discuss the long-term peace and sustainable economic developments on the autonomous Danish territory.

However, escalating tensions with Iran saw that trip cancelled.

Greenland rejects notion of sale to the US

Greenland's government on Friday dismissed the idea it was for sale.

'We are open for business, but we're not for sale,' Greenland's foreign minister Ane Lone Bagger told Reuters.

'#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,' the official account of the Ministry of Foreign Affairs tweeted.

It's unclear how exactly the US would go about buying the largest island in the world after two failed attempts in 1946 and 1867

Other Danish politicians also scorned the idea.

'It has to be an April Fool's joke. Totally out of season,' former prime minister Lars Lokke Rasmussen wrote on Twitter.

'If he is truly contemplating this, then this is final proof, that he has gone mad,' foreign affairs spokesman for the Danish People's Party, Soren Espersen, told broadcaster DR.

'The thought of Denmark selling 50,000 citizens to the United States is completely ridiculous,' he added.

Officials with the Denmark's Royal House and the Danish embassy in Washington have yet to respond to the Wall street Journal's request for comment on the matter.

Twitter users reacted with scorn and derision to the notion of Trump considering a deal to buy Greenland.

Actress Bette Midler wrote: 'Trump wants to buy Greenland? Let’s make him find it on a map first.'

Meanwhile writer Jon Gabriel posted an image of a town in Greenland with a huge golden Trump Tower photoshopped in, with the caption: 'Greenland in 10 years.'

History of US territorial expansion

The United States has a long history of acquiring territory since it was first established as an independent nation state.

The end of the American Revolution with the 1783 Treaty of Paris and Great Britain ceding the area of its thirteen colonies saw the beginning of the United States' territorial acquisitions.

According to the United States Geological Survey the new nation went on for the next few decades to gradually add new territory until it reached the size it is today.

Alongside the territory that makes up its mainland the United States has control of a number of territories in its nearby waters and a number further afield in the Pacific and Asia.

Among its key purchases, was that of Louisiana, which the Global Policy Forum said it bought in 1803 from France for $15 million, the equivalent of $193 million in 2005.

The Republic of Texas agreed to be annexed by the United States in 1845, effectively bringing in 389,000 square miles of what was once Mexican territory under its control.

Three years later, after the Mexican-American War, all of the present-day states of California, Nevada, and Utah, as well as sections of Arizona, Colorado, New Mexico and Wyoming were ceded to the US by Mexico.

A view of Douglas Island and the Gastineau Channel in southeast Alaska. The country came under United States rule in 1867 after it was bought from Russia

And in 1867 the United States bought Alaska, from Russia, for $7.2 million.

Further afield, American Samoa became a US territory under the 1899 Treaty of Berlin between Germany, Great Britain, and the United States.

The islands to this day are under the administration of the U.S. Department of the Interior, Office of Insular Affairs alongside Guam, which has been under its administration since the Spanish-American War of 1898 - barring three years during World War Two when Japan took control.

Today, there are also a number of outlying islands, which are territories of the United States, including the Midway Atoll, (1867), Palmyra Atoll (1898, with Hawaii), Wake Atoll (1899), Baker Island and Howland Island ( 1857), Jarvis Island ( 1858), Johnston Atoll (1858), Kingman Reef (1922), and Navassa Island (1857).