Trump considers buying Greenland. Can he do it?

Trumps says he is considering buying Greenland
President Donald Trump on Sunday confirmed that he has talked with some about purchasing Greenland.

But, Trump told reporters, it's not on the front burner.

“Strategically, for the United States, it would be nice,” Trump said. “Essentially, it’s a large real-estate deal.”
National Economic Council Director Lawrence Kudlow was asked on Fox News Sunday if it was true that Trump was considering buying Greenland. 
 “Denmark is an ally,” Kudlow said. Greenland is a strategic place up there … I don’t want to predict it now. I’m just saying the president, who knows a thing or two about buying real estate, wants to take a look at a potential Greenland purchase.
Why would the president be interested in buying the island? Here’s a look at Greenland, and why Trump would want it.
Where is Greenland?
Greenland is northeast of Canada and northwest of Iceland. It is located between the Arctic Ocean and the North Atlantic Ocean.
Greenland is considered the world’s largest island.
Is Greenland a country?
No, Greenland is not a sovereign country.
Which country owns Greenland?
Greenland is owned by Denmark. However, it does have its own autonomous government a parliament.
Is Greenland really green?
Not really. Eighty percent of the island is covered in ice.
Iceland, on the other hand, is fairly green.
Is it for sale?
Leaders in Greenland say no. The current government in Denmark says no, and former Danish Prime Minister Lars Lokke Rasmussen said of the idea, "It must be an April Fool's Day joke."
What does Trump want with Greenland?
Greenland has an abundance of natural resources and its location could make it a strategic military asset.
According to the CIA World Factbook, the country is rich in coal, iron ore, lead, zinc, molybdenum, diamonds, gold, platinum, niobium, tantalite, uranium, fish, seals, whales, hydropower, possible oil and gas.
The United States already has an airbase, Thule Air Base, on the island, along with a radar station that is part of a U.S. ballistic missile early-warning system.  
How could the U.S. buy it?
According to The Wall Street Journal, it is not clear how the U.S. would go about purchasing Greenland should Denmark decided to sell the island.  
Has the U.S. ever tried to buy Greenland before?
The U.S. has considered purchasing Greenland at least three times in the past. The idea was first floated during Andrew Jackson’s administration in the 1830s, then in 1867, a State Department report suggested that the U.S. purchase both Greenland and Iceland.
In 1946, President Harry Truman offered Denmark $100 million in gold for Greenland.
Has the U.S. purchased land from Denmark before?
Yes. The U.S. purchased the Virgin Islands from Denmark in 1917.
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