Why are Vikings such common mascots in American sports?

Vikings are strong, and seem to not have mercy. They go after what they want even if it means pillaging through towns. In American sports, teams want to be portrayed as a strong force so why not look to the Vikings as an example? When you think of vikings you think of strong, fearless men with big hats and horns on them. It is no wonder that one would want to be seen as this.