Beginning of the Kingdom
"The Danish Vikings were most active in the British Isles and Western Europe. They conquered and settled parts of England (known as the Danelaw) under King Sweyn Forkbeard in 1013, Ireland, and France where they founded Normandy. More Anglo-Saxon pence of this period have been found in Denmark than in England.
Larger of the two Jelling stones, raised by Harald Bluetooth.
As attested by the Jelling stones, the Danes were united and Christianised about 965 by Harald Bluetooth. It is believed that Denmark became Christian for political reasons so as not to get invaded by the rising Christian power in Europe, Germania, which was an important trading area for the Danes. In that case Harald built six fortresses around Denmark called Trelleborg and built a further Danevirke. In the early 11th century, Canute the Great won and united Denmark, England, and Norway for almost 30 years." – []
History and the Merge with Sweden
Denmark had had a history of military strength and power, but could only handle poor and dying kingdoms. In the early 13th century, Denmark fought a series of wars where they attempted to capture the kingdom of Norway. They captured the whole of it by 1222, which only brought up it's force and population.
In the mid 14th century, during the heart of the renaissance, Sweden began meetings with Denmark to bring up morale. During this time, Sweden brought up high relations with Denmark, which led to them merging into the Kingdom of Denmark-Sweden by 1384. It was a kingdom with two kings, one from each former kingdom.