German–Danish War of 974

The German–Danish War of 974, also known as the Rebellion of Harald Bluetooth, was a conflict between Denmark, under the newly established House of Knýtlinga, and the Holy Roman Empire, under the Ottonian Dynasty.

The Ottonians, specifically under Otto the Great, sought to crush the rebellion of the Danish king, Harald Bluetooth, to secure Otto's position and ensure stability in preventing Viking raids.

War
When Otto died in 973, King Harald leaped at the opportunity to free his people from the imperial shackles. He, along with the Norwegians, formally rebelled against the new emperor, Otto II. Before long, a Viking army once more invaded and ransacked Saxony, the heartland of the "Ottonian" imperial dynasty.

The Holy Roman Empire responded as fast as it could. Emperor Otto II led an army to Denmark; he met heavy resistance, and Emperor Otto II was defeated at the gate of Wiglesdor at Dannevirke to both monarchs' surprise.

The Norwegians returned home after the battle, leaving the Danes to fend for themselves. Otto II sensed an opportunity for revenge and attacked Harald’s army the next year. This time, the imperial military was successful.

After beating the Danes in battle, the enemy broke through the Danevirke. For the first time in history, soldiers of the Empire were on the northern side of the wall. To Harald’s great detriment, Otto II also conquered parts of Jutland in the wake of this catastrophe.

Aftermath
Defeated, Harald once again submitted to the Ottonians.

Earl Haakon had helped against the Germans with a Norwegian army, but shortly after the Danish defeat and Harald forcing him to convert to Christianity, he rebelled against Harald Bluetooth in 975 and made Norway an independent kingdom.