Greenland became part of Denmark through a long chain of medieval unions, colonial claims, and later constitutional changes that turned an old colony into an autonomous part of the Danish realm. The short version: it moved from Norway to the joint Danish–Norwegian crown, then stayed with Denmark when that union split, and was later integrated (and partially decolonized) inside the modern Kingdom of Denmark.

Viking and Norwegian beginnings

  • Norse settlers from Iceland and Norway colonized parts of Greenland around the late 10th century, bringing the island into the Norwegian sphere of influence.
  • By the late Middle Ages, Greenland was regarded as a Norwegian dependency; when the Norwegian crown entered a union with Denmark, Greenland came with it.

Denmark–Norway and colonial revival

  • In 1380, Norway came under the Danish crown, so Norway’s overseas possessions, including Greenland, effectively became part of the Danish-led union (often called Denmark–Norway).
  • After the medieval Norse settlements collapsed, Scandinavian contact faded until 1721, when missionary Hans Egede, backed by the joint Danish–Norwegian monarchy, re‑established a permanent European presence and trade monopoly in Greenland.

From Norway’s loss to Danish control

  • The Denmark–Norway union broke up in 1814 after the Napoleonic Wars; Norway was ceded to Sweden, but Denmark kept Norway’s former colonies, including Greenland, Iceland, and the Faroe Islands.
  • During the 19th and early 20th centuries Denmark tightened its colonial administration, and in 1916 the United States formally recognized Danish sovereignty over Greenland as part of a treaty involving the sale of the Danish West Indies.

Legal confirmation and end of colonial status

  • A Norwegian attempt to claim parts of eastern Greenland led to a case at the Permanent Court of International Justice, which ruled in 1933 that Greenland belonged to Denmark as a whole, reinforcing Danish sovereignty.
  • In 1953, a new Danish constitution ended Greenland’s legal status as a colony and incorporated it into Denmark as a county; Greenlanders were made full Danish citizens under this framework.

Home rule and today’s relationship

  • Growing Greenlandic nationalism and decolonization trends led Denmark to grant home rule in 1979, giving Greenland its own parliament and government while remaining under the Danish crown.
  • A 2009 self‑government act transferred more powers (including control over most natural resources) to Greenland and recognized Greenlanders as a distinct people under international law; Denmark still handles defense, foreign policy, and the monarchy, which is why Greenland is today an autonomous territory within the Kingdom of Denmark rather than an independent state.

TL;DR: Greenland became part of Denmark because it was first a Norwegian possession, then part of the Denmark–Norway union, and when that union split in 1814, Denmark kept Greenland and later converted its colonial rule into an autonomous-but-still-Danish constitutional relationship.

Information gathered from public forums or data available on the internet and portrayed here.