In the year 793, Danish Vikings attacked Lindisfarne on the Northeast coast of England and thereby marked the beginning of the Viking Age. During the following centuries the Danes played an important role in the Viking raids on Flemish, English and French coastal trading stations, and soon they also began settling in these areas.

The Danish monarchy, the world's oldest, can with certainty be traced back to King Gorm the Old (d. 958). About the year 960, the Danes were converted to Christianity and Gorm’s son, Harald Bluetooth, became the first Christian king of Denmark. On his famous rune stone in Jelling, which features an image of Christ, the word "Denmark" appears for the first time. Harald's son, Sweyn Forkbeard, later conquered England and from 1018 to 1035, Denmark, England, and Norway were united under King Canute the Great. After Canute's death, during the years of Canute the Holy and Eric Egode, Denmark fell into a period of turmoil and civil war, and both England and Norway slipped away. The Norman invasion of England in 1066 usually marks the end of the Viking Age.

During the later Great Period of the Waldemars (Waldemar the Great and Waldemar the Victorious) Danish hegemony was established over a great part of Northern Europe. According to legend, it was in the course of the Battle of Lyndanisse in Estonia that a red flag bearing a white cross floated down from heaven - a 'sign from God'. A strong and independent church developed, and, due to the later weak kings, the nobles forced King Eric to sign 'The Royal Charter' in 1282, thereby establishing a form of government where the king had to collaborate with the nobles and where an annual national assembly had to be called.

Rex Danorum (King of the Danes): By the grace of God king of Denmark, Norway, the Goths, and the Wends, duke of Schleswig, Holstein, Stormarn, and Ditmarschen

Waldemar Atterdag, who reigned 1340-75, brought Danish power back to a high point, and in 1397 the Danish, Norwegian, and Swedish crowns were united in the Kalmar Union under his daughter, Queen Margaret. In 1460, Christian I united Schleswig and Holstein with the Danish crown. However, Sweden escaped the Danish rule in 1523 and the union was dissolved. The southern part of Sweden (Scania, Halland, and Blekinge) was, with brief interruptions, part of Denmark until 'The Treaty of Roskilde' in 1658, but the union with Norway lasted until 1814, when Norway became a part of Sweden.

The Lutheran Reformation came to Denmark in 1536, and, after that, Lutheranism became the established religion. In the centuries that followed, 'The Royal Charter of 1282' (the division of power between the Danish king and the nobles) seriously weakened the attempt to gain supremacy in the region. Denmark was involved in numerous wars, mainly with Sweden, and in the aftermath of the 'Thirty Years War' and the later wars, a peace treaty was signed in Roskilde in 1658. This meant that a third of the Danish territory was lost. Despite the treaty, the Swedish king did not withdraw his troops from Denmark, so the fighting began once more. However, after the siege of Copenhagen and the following Danish defeat, the Danish-Swedish 'Treaty of Copenhagen' 1660 was signed, confirming most of the territorial losses; Denmark had lost its hegemony to Sweden.

During the preceding years of war, the nobility had been weakened significantly allowing the monarchy to be strengthened during the reigns of Frederick III and Christian V. With the support of the peasants and townspeople in Denmark, absolute monarchy was established. In the following period, Denmark maintained an imperial status with the continuous rule over Iceland and by establishing colonies and trading stations in Tranquebar (in present day India), the Danish Gold Coast (in present day Ghana) and the Danish West Indies (the US Virgin Islands). Furthermore, the ducal and the royal part of Schleswig were united during the reign of Frederick IV, 1699-1730. Important social reforms were introduced toward the end of the 1700s leading to the 'liberation of the peasants' - the abolishment of serfdom in 1788. Instead, peasant proprietorship was encouraged. In 1792 Denmark became the first country in the world to abolish slave-trading.