Final answer:
The brutal invaders to Britain in the 800s were the Vikings, who were noted for their sudden and violent raids on settlements, particularly targeting locations like monasteries for valuables. Over time, they settled in various parts of Britain, establishing a significant presence that influenced trade and culture.
Step-by-step explanation:
The brutal invaders to Britain in the 800s were the Vikings, originating from Scandinavia. These Norse raiders were known for their sudden and violent raids, striking fear into the populations of western Europe with their tactics of attacking in small groups and targeting poorly defended locations such as churches and monasteries, where they could plunder valuables. A well-known raid by the Vikings was the destruction of the monastery of Lindisfarne in the Anglo-Saxon kingdom of Northumbria, which was a respected center of learning. Eventually, the Vikings began to settle in the territories they raided, which included large parts of Britain.
By the end of the 800s, the Vikings had established settlements throughout the British Isles, influencing trade, culture, and the political landscape of the region. Their presence was so significant that they even established a Viking kingdom in eastern England. The last Anglo-Saxon kingdom, Wessex, was able to repel the Viking invaders by 879, but the Viking influence remained eminent through ongoing raids and eventual settlement in various parts of the country.