Greenland is the world's largest island, situated east of the Canadian Arctic Archipelago, between the Arctic and Atlantic oceans. Greenland is a self-governing region within the Danish Kingdom. Despite being geographically part of North America, Greenland has been politically and culturally linked to Europe for over a millennium, dating back to 986. The majority of the island's inhabitants are Inuit, whose ancestors migrated from Alaska through Northern Canada, eventually settling across the island by the 13th century. Today, the population is concentrated mostly on the island's southwest coast, with the remainder of the island sparsely inhabited. Sermersooq, Kujalleq, Qeqertalik, Qeqqata, and Avannaata are the five municipalities that make up Greenland. The Northeast Greenland National Park and the Thule Air Base are also unincorporated territories. While the former is under Danish jurisdiction, the latter is administered by the US Air Force. The largest permanent ice sheet outside of Antarctica covers three-quarters of Greenland. It is the world's least densely populated area, with a population of 56,081. Nuuk, the capital and largest city, is home to about a third of the population; Sisimiut, 320 kilometers north of Nuuk, is the second-largest city by population. The Arctic Umiaq Line ferry connects the numerous cities and settlements in western Greenland, serving as a lifeline. Greenland has been populated by Arctic peoples whose forefathers migrated there from what is now Canada at various times over the last 4,500 years. Norsemen, who had previously settled Iceland, began settling the uninhabited southern part of Greenland in the 10th century. These Norsemen sailed from Greenland and Iceland later, with Leif Erikson becoming the first documented European to reach North America nearly 500 years before Columbus reached the Caribbean islands. In the 13th century, Inuit people arrived. Greenland was not officially under the Norwegian crown until 1261, despite being constantly influenced by Norway and Norwegians. The Norse colonies vanished in the late 15th century, when Norway was devastated by the Black Death and fell into a state of decline. Following their demise in 1499, the Portuguese briefly explored and claimed the island, calling it Terra do Lavrador. Danish explorers returned to Greenland in the early 17th century. Denmark and Norway affirmed jurisdiction over the island in order to boost trade and influence. Norway lost sovereignty over Greenland in 1814 when the union was dissolved due to its low status. Greenland joined Denmark in 1814 and was fully incorporated in 1953, according to the Danish constitution. Greenlanders became Danish citizens in 1953, thanks to the Constitution. Greenland joined the European Free Trade Association in 1961, after Denmark joined as a founding member of the EFTA in 1960. However, Greenland's membership ended in 1973 when Denmark joined the European Communities.