During the Viking period (9th-11th centuries), Denmark was a great power based on the Jutland Peninsula, the Island of Zealand, and the southern part of what is now Sweden. In the early 11th century, King Canute united Denmark and England for almost 30 years. | During the Viking period (9th-11th centuries), Denmark was a great power based on the Jutland Peninsula, the Island of Zealand, and the southern part of what is now Sweden. In the early 11th century, King Canute united Denmark and England for almost 30 years. |