Life after Charlemagne's death.
After Charlemagne passed away, everything went downhill from there. Starting with Invasions, then the empire was divided by his three grandsons, and Nobles gained power.
Not only that, but counterurbanisation came into play. Counterurbanization is basically when people in urban areas move to rural areas. This of course, led to a high decrease in population. Most people either stayed or moved to Europe.
Vikings
They left for a reason, of course. Not just because the empire has basically fallen, but invasions became a huge issue. Mainly by Vikings, who were Germanic people who seeked fortune, adventure, and war. They were also amazing ship builders, who could carry around 50 men per ship. The Frankish Lands saw this as a threat. So, they decided to keep the peace by giving them a portion of land, now known as Normandy, and converted them to Christian. This resulted in letting Vikings settling in Europe as they are also Christians.
