The United States has bought land to increase its territory several times. On August 25th, 1829, President Andrew Jackson offered to buy Texas from Mexico. Two years previously, his predecessor, John Quincy Adams, had tried to buy it from Mexico for $1m. Now Andrews Jackson’s aide, Col Anthony Butler, tried to bribe Mexico’s Santa Anna, but he far exceeded his authority, and Jackson recalled him. Jackson was reportedly prepared to go “as high as $5m,” but Mexico would have none of it.

It was not the first such transaction. The Louisiana Purchase of 1803 had bought 828,000 square miles of France’s American territories from a cash-strapped Napoleon for $15m. This effectively doubled the size of the United States, acquiring land that stretched from Louisiana in the South to Montana in the North. Jackson had thought this included Texas, but a previous Florida Treaty had left that to Mexico. After Jackson’s offer was rejected, the Texans eventually declared their independence from Mexico, and General Sam Houston’s army defeated that of Santa Anna. The independent Texas was later annexed in 1845 as part of the United States, without Mexico receiving any money for it.

The US had previously extended its territory in 1818 by securing the Red River Valley without payment by agreement with the British. In the 1819 Florida Purchase, Spain ceded lands in Florida and Louisiana, but since the US assumed $5 million in claims by US citizens against Spain, no money actually changed hands.

The 1853 Gadsden Purchase bought land within what is now Arizona and New Mexico from Mexico for $10m. And in 1867, the US bought Alaska from Russia for $7.2m. The US finalized a deal with Denmark in 1917 to buy the Virgin Islands after a referendum in Denmark had assented to the deal.

In the context of this history, President Donald Trump’s expressed interest in purchasing Greenland is in a long tradition of American territorial purchases. The US first offered to buy Greenland from Denmark in 1946 for the sum of £100m, but the Danes declined. From the US point of view, such a purchase would make sense, given Greenland’s strategic location and resource development potential. America does not want Chinese investment increasing its influence so close to the US’s own doorstep.

From Greenland’s point of view, acquisition by the US would have some attractions. US finance and knowhow could help to augment the island’s wealth and improve the lives of its peoples. Obviously, any such deal would require the consent of the Greenlanders, as well as that of the Danish government, and it might be wise to include a clause promising that the territory would proceed at some stage to the status of a state within the Union, instead of remaining a protectorate or dependency.

The proposed deal would be well within the tradition of America’s previous stages of expansion, and is by no means as outlandish as much of the media have suggested. Denmark has said no, but the intriguing question is whether there is a price at which they would say yes.