Why is it believed that Denmark became Christian ?
This includes : The Kingdom of Denmark ( up to 1397 ) * Personal union of Denmark and Norway ( 1380–1397 ) The Kalmar Union ( 1397–1536 ) * Union of Denmark , Norway and Sweden ( 1397–1523 ) * Union of Denmark and Norway ( 1523–1536 ) The Kingdom of Denmark - Norway ( 1536–1814 ) The Kingdom of Denmark ( 1814 to present ) * Iceland ( since the union between Denmark and Norway in 1380 .