The unified kingdom of Denmark emerged in the 10th century as a proficient seafaring nation in the struggle for control of the Baltic Sea. Denmark, Sweden and Norway were ruled together under the Kalmar Union, established in 1397 and ending with Swedish secession in 1523. Denmark and Norway remained under the same monarch until outside forces dissolved the union in 1814. The union with Norway made it possible for Denmark to inherit the Faroe Islands, Greenland and Iceland. Beginning in the 17th century, there were several cessions of territory to Sweden. In the 19th century there was a surge of nationalist movements, which were defeated in the 1864 Second Schleswig War. Denmark remained neutral during World War I. In April 1940, a German invasion saw brief military skirmishes while the Danish resistance movement was active from 1943 until the German surrender in May 1945. An industrialised exporter of agricultural produce in the second half of the 19th century, Denmark introduced social and labour-market reforms in the early 20th century that created the basis for the present welfare state model with a highly developed mixed economy.
The Constitution of Denmark was signed on 5 June 1849, ending the absolute monarchy, which had begun in 1660. It establishes a constitutional monarchy organised as a parliamentary democracy. The government and national parliament are seated in Copenhagen, the nation's capital, largest city and main commercial centre. Denmark exercises hegemonic influence in the Danish Realm, devolving powers to handle internal affairs. Home rule was established in the Faroe Islands in 1948; in Greenland home rule was established in 1979 and further autonomy in 2009. Denmark became a member of the European Economic Community (now the EU) in 1973, maintaining certain opt-outs; it retains its own currency, the krone. It is among the founding members of NATO, the Nordic Council, the OECD, OSCE, and the United Nations; it is also part of the Schengen Area.
Denmark is considered to be one of the most economically and socially developed countries in the world. Danes enjoy a high standard of living and the country ranks highly in some metrics of national performance, including education, health care, protection of civil liberties, democratic governance, prosperity and human development. The country ranks as having the world's highest social mobility, a high level of income equality, is the country with the lowest perceived level of corruption in the world, the fifth-most developed in the world after Germany, has one of the world's highest per capita incomes, and one of the world's highest personal income tax rates.
The etymology of the word Denmark, and especially the relationship between Danes and Denmark and the unifying of Denmark as a single kingdom, is a subject which attracts debate. This is centred primarily on the prefix "Dan" and whether it refers to the Dani or a historical person Dan and the exact meaning of the -"mark" ending.
Most handbooks derive the first part of the word, and the name of the people, from a word meaning "flat land", related to German Tenne "threshing floor", English den "cave". The -mark is believed to mean woodland or borderland (see marches), with probable references to the border forests in south Schleswig.