Two centuries of Viking
raids into Europe tapered off following the adoption of Christianity by
King Olav Tryggvason in 994. Conversion of the Norwegian kingdom
occurred over the next several decades. In 1397, Norway was absorbed
into a union with Denmark that lasted more than four centuries. In
1814, Norwegians resisted the cession of their country to Sweden and
adopted a new constitution. Sweden then invaded Norway but agreed to
let Norway keep its constitution in return for accepting the union
under a Swedish king. Rising nationalism throughout the 19th century
led to a 1905 referendum granting Norway independence. Although Norway
remained neutral in World War I, it suffered heavy losses to its
shipping. Norway proclaimed its neutrality at the outset of World War
II, but was nonetheless occupied for five years by Nazi
Germany (1940-45). In 1949, neutrality was
abandoned and Norway became a member of NATO. Discovery of oil and gas
in adjacent waters in the late 1960s boosted Norway's economic
fortunes. In referenda held in 1972 and 1994, Norway rejected joining
the EU. Bokmal Norwegian and Nynorsk Norwegian are the official
languages.