Denmark was first united in the 10th century, during the Viking period, by the king Harald Bluetooth (), who first converted Denmark to Christianity. The Vikings are well known for invading countries. In the 11th century, the Danish Vikings controlled England (the Danelaw) for a while. In 1397 Denmark, Sweden and Norway became a single country with one queen (this country was called the "Kalmar Union") Sweden became a separate country again in 1523. Denmark and Norway (called "Denmark-Norway)" stayed united, until 1814. Denmark-Norway controlled many islands in the Atlantic Ocean, including the Faroe Islands, Iceland and Greenland. Iceland became independent from Denmark in 1944.