How could the US acquire Greenland?

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President Donald Trump has made very clear his desire to “acquire” Greenland from Denmark, no matter the damage to NATO or to the US alliance with Europe.

What the White House has not done is spell out how Trump’s acquisition would take place. While Trump has not ruled out using the military, it would be an unprecedented use of the modern military to invade and claim for the US a semiautonomous territory despite domestic and international opposition. Two exceptions are the 1893 US-backed coup in Hawaii, something for which the US government apologized in 1993, and the bloody three-year Philippine-American War in 1899, when the US put down a rebellion by Filipinos after it took control of the Philippines from Spain.

The text of the Constitution and the example of history suggest that for a more peaceful option, Trump would need to ratify a treaty with Denmark and Greenland to buy the world’s largest island.

Ratifying a treaty, according to the Constitution, requires 67 senators, which in today’s political environment means Trump would have to convince Republicans and some Democrats to back him. He would also have to squeeze money for the purchase out of Congress. Meanwhile, some senators from both parties have introduced legislation to protect NATO by blocking Trump from acquiring Greenland.

A brief history of the US buying land from Denmark

Trump seems unlikely to let opposition in Congress get him down, so consider the 50-year odyssey required for the US to obtain what today are known as the US Virgin Islands … from, coincidentally, Denmark.

The US, led by then-Secretary of State William Seward, realized the strategic importance of the islands during the Civil War and tried to purchase the islands from a willing Denmark for $7.5 million. The two sides negotiated a treaty, which was approved by a vote in Denmark.

But the 1867 sale did not ultimately go through, according to a US State Department history, because the Senate failed to ratify the treaty. Without going too deep into the historical details, senators were angry at Seward over his support for the impeached President Andrew Johnson.

Today Trump has neither a purchase price nor the willing cooperation of Denmark or Greenland, much less a willing Senate.

It took three tries for the US to buy the Virgin Islands from Denmark

In the early part of the 20th century, the US Senate did approve a treaty with Denmark to buy the islands, but this time the deal failed because the Danish parliament did not sign on.

It was not until World War 1 loomed that the US essentially threatened to occupy the islands. That threat was enough to make the sale happen, for $25 million in gold coin. The Senate approved the treaty in September of 1916 after the Danish parliament, its king, and a plebiscite (which is a fancy word for a direct election for all eligible voters) also approved. No vote was held for the islanders to weigh in, according to the State Department history.

The Constitution gives the president the power “by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur….”

Two-thirds of senators is a high bar — 67 if all senators are present and voting, which means Trump would need the support of some Democrats. But even some Republicans — among them Sen. Lisa Murkowski of Alaska, which the US bought from Russia for $7.2 million in 1867 — have expressed grave doubts about Trump’s Greenland plan.

The requirement of 67 senators to approve treaties may have something to do with the fact that presidents in recent decades have entered into agreements with foreign countries without offering them to the Senate for approval. These types of agreements are still binding under international law, but they have not been used to obtain territory.

The Constitution also gives Congress, not the president, the power to dispose of and manage federal lands and territories, although the executive branch conducts much of that business on a day to day basis.

The Louisiana Purchase and Thomas Jefferson’s example

When President Thomas Jefferson doubled the size of the US with the Louisiana Purchase (thanks, France), he worried he was exceeding his constitutional authority since the Constitution says nothing about acquiring lands. But he sent the agreement to the Senate anyway, and it was approved.

In separate legislation, legislators approved the creation of a special stock to finance the $15 million purchase price. That seems like a steal today for land that would become Louisiana, Arkansas, Missouri, Iowa, Oklahoma, Kansas, Nebraska, North Dakota, South Dakota, Minnesota, New Mexico, Montana, Wyoming, and Colorado. It’s also hard to imagine the people in those states speaking French.

It took another treaty — the Adams-Onis treaty, this time with Spain and finalized in 1821 — for the US to clarify the boundaries of the Louisiana Purchase. The US got Florida and Spain got Texas, which it held until 1836.

Seward’s follies almost included Greenland

Around the same time he was trying to buy the Virgin Islands, Seward successfully bought Alaska after the Senate approved that purchase from Russia. It was derided by critics at the time as “Seward’s folly,” but has aged extremely well given the discovery of gold and oil there.

CNN’s Lex Harvey notes that Seward also tried to obtain Greenland. Later, the US considered a trade with Denmark to obtain Greenland, but the effort didn’t go anywhere.

Grover Cleveland revoked his predecessor’s annexation treaty

President Benjamin Harrison signed a treaty to annex Hawaii after a group of US businessmen trying to avoid tariffs launched a coup in the 1890s. But the Senate did not consider it because it was withdrawn after Grover Cleveland, the only president besides Trump to serve nonconsecutive terms, reclaimed the White House in 1893. Hawaii would not be officially annexed until William McKinley took office.

Not included in the 1898 Treaty of Paris, which ended the war with Spain and netted the US the Philippines and Puerto Rico, was the sale of Cuba to the US. Americans had supported Cuba in its rebellion against Spain and lawmakers even passed legislation promising not to exert control over Cuba after the war.

The US immediately broke that promise, however, and occupied Cuba for the first of several times starting in 1899. US Lawmakers passed legislation — the Platt Amendment — that gave the US paternalist control over Cuba and led to the establishment of military bases, including Guantanamo Bay.

The US military is already in Greenland with an option to grow

Under existing agreements with Denmark and Greenland, the US has the ability to drastically increase its military presence in Greenland, but Trump has said he would prefer to own Greenland.

Any such ownership would require the assent of Greenlanders under the UN charter – although Trump may not think that international law applies to the US – but he will have more trouble arguing the Constitution does not, and it has required Senate approval for the acquisition of territories for hundreds of years.