The complex lengthy history of Vikings and their culture can be summed up by this image.
Vikings, also known as Norsemen, were a loose-knit group of raiders, explorers and merchants from Scandinavia, also known as the part of Europe that is cold, all the time. Because of their natural habitat, Vikings could never really get a good handle on the whole "sedentary agriculturalism" that was all the craze in the rest of Europe. So, much like many of us do, they lived by taking things from people with actual jobs, except instead of your parents, the Vikings took from everybody within 10 miles of the coast.
Where are the Pringles?
What allowed the Vikings to do this was the fact that they were: 1. The best boat engineers and sailors in the world, and 2. fucking massive.
When we say that the Vikings made the best boats, we aren't exaggerating. Their longships were decades ahead of anything the rest of Europe had, capable of going faster and farther than anything in the sea that wasn't a super fish.
Not only could the Vikings show up just about anywhere on the coast, the longships were small enough that they could sail up rivers too. Since almost all prosperous towns of the time were either on the shore or on a river, said towns could rely on nothing but their own warriors to defend them from Vikings.
And those warriors had to fight this:
This is Ulf Bearpuncher. He never lived up to the Viking standard of manliness.
Your average Viking stood about a foot taller than most men, and were completely and utterly ripped. This is because Viking men did three things: row boats, fight, and feast on the biggest animals they could find. Viking warriors were taught to not fear death, because they knew that if they died in combat, they would go to Valhalla, Viking heaven. Guess what you got to do in Valhalla? Fight, feast, and bang Valkyries.
No, not that Valhalla. But the Viking afterlife is a lot like a big game of Halo, but with women.
To sum up, imagine the scariest gang in existance. Now give them the flying cars from Back to the Future. To Medieval Europeans, those were the Vikings.
Where we're going, we don't need fjords.