Final answer:
The Vikings posed the greatest military threat to Europe during the Middle Ages due to their expert seafaring skills, frequent raids, and ability to establish settlements far into Eastern Europe.
Step-by-step explanation:
The greatest military threat to Europe during the Middle Ages came from the Vikings. The Vikings, also known as Norse, were a group of Northern European raiders who attacked and pillaged various parts of Europe. They were known for their expert seafaring skills and frequent raids on coastal areas.
One of the reasons the Vikings posed the greatest threat was their ability to navigate rivers with their shallow-drought ships, allowing them to establish settlements far into Eastern Europe and even reach as far as Constantinople. They were relentless in their plundering and trading activities, which made them a formidable military force.
Although there were other threats during the Middle Ages, such as the Goths, Muslims, and Huns, the Vikings were the most significant invaders and posed the greatest military threat to Europe.