Perspective

“In many respects the Vikings were the medieval equivalent of organized crime,” says Simon Keynes, a professor of Anglo-Saxon history at Cambridge University. “They engaged in extortion on a massive scale, using the threat of violence to extract vast quantities of silver from England and some other vulnerable western European states.”

“Certainly the Vikings did all these things, but so did everyone else,” says Dagfinn Skre, a professor of archaeology at the University of Oslo. “Although admittedly, the Vikings did it on a grander scale.”

Also: Dublin, one of the largest Viking cities in the British Isles, became a major European slave-trading center, where, historians estimate, tens of thousands of kidnapped Irishmen, Scotsmen, Anglo-Saxons and others were bought and sold.

http://www.smithsonianmag.com/history-archaeology/A-Viking-Mystery.html?c=y&page=1

One thing leads to another thing and that to another and first thing you know, William of Normandy is king.