The biggest enemy of the Vikings is often considered to be the Saxons, particularly during the reign of King Alfred the Great in the late 9th century.
During this period, the Vikings launched numerous raids into England, targeting the wealth and resources of the Saxon kingdoms. The Saxons, led by Alfred, were able to unite various factions to create a stronger defense against these raids. Alfred’s successful strategies at the battles of Edington and Athelney significantly weakened Viking influence in the region.
Additionally, the Franks, under Charlemagne, posed a significant threat to Viking ambitions in continental Europe. The Carolingian Empire’s military might and fortifications hindered Viking expansion into territories that were otherwise rich in opportunities.
In summary, while the Vikings faced multiple adversaries, the Saxons and the Franks stood out as their most formidable and persistent enemies during their age of exploration and conquest.