Viking raid warfare and tactics
Vikings were members of tribes, originally from Scandinavia, of Norse ancestry, who gained a reputation for their raids and piracy in many parts of Europe, especially England, Ireland, and Frankish territories. The term "Viking Age" refers to the period roughly from 793 AD to the late 11th century in Europe. In this era Viking activity started with raids on Christian lands in England and eventually expanded to mainland Europe, including parts of present-day Russia. While maritime battles were rare, Viking bands proved very successful in raiding coastal towns and monasteries due to their efficient warships, and intimidating war tactics, skillful hand-to-hand combat, and fearlessness. What started as Viking raids on small towns transformed into the establishment of important agricultural spaces and commercial trading-hubs across Europe through rudimentary colonization. Vikings' tactics in warfare gave them an enormous advantage in successfully raiding (and later colonizing), despite their small population in comparison to that of their enemies.
Denmark
From the 8th to the 10th century the wider Scandinavian region was the source of Vikings. They colonised, raided, and traded in all parts of Europe. The Danish Vikings were most active in the eastern and southern British Isles and Western Europe. They conquered and settled parts of England (known as the Danelaw) under King Sweyn Forkbeard in 1013, and France where Danes and Norwegians founded Normandy with Rollo as head of state. More Anglo-Saxon pence of this period have been found in Denmark than in England.
Denmark was largely consolidated by the late 8th century and its rulers are consistently referred to in Frankish sources as kings ("reges"). Under the reign of Gudfred in 804 the Danish kingdom may have included all the lands of Jutland, Scania and the Danish islands, excluding Bornholm.
The extant Danish monarchy traces its roots back to Gorm the Old, who established his reign in the early 10th century. As attested by the Jelling stones, the Danes were Christianised around 965 by Harald Bluetooth, the son of Gorm. It is believed that Denmark became Christian for political reasons so as not to get invaded by the rising Christian power in Europe, the Holy Roman Empire, 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 with a Scandinavian army.