Greenland is the source of many of the weather changes in the northern hemisphere, and knowledge of Greenland weather is of prime importance for the prediction of conditions in the North Atlantic Ocean and in western Europe. Weather and radio stations are of inestimable value for Atlantic air traffic. In 1944, during World War II, a German radio-weather station on the northeast coast was destroyed by the U.S. Coast Guard, and various German attempts to establish weather bases on Greenland were thwarted by Coast Guard vessels. In May 1947, Denmark requested that the United States end the 1941 agreement.By the terms of other provisions,the armed forces of the North Atlantic Treaty Organization were authorized to use all naval, air, and military bases on the island. In the early 1950s the United States expanded its military operations in Greenland, constructing a large strategic air base at Thule, about 1,500 km from the North Pole.

The United States relinquished its claim to land in northern Greenland, based on the explorations of the American explorer Robert Edwin Peary, when it purchased the Virgin Islands from Denmark in 1917. In May 1921, Denmark declared the entire island of Greenland to be Danish territory, causing a dispute with Norway over hunting and fishing rights. In 1931 a strip of land on the east coast was claimed by some Norwegian hunters, whose action was later recognized by the Norwegian government. The occupation was invalidated by the Permanent Court of International Justice at The Hague in 1933.