Before the war of ninjas and pirates was even an idea in the heads of prideful people.
Vikings ruled the seas. And not just the sea. They struck like a hurricane, devastating the coastal cities and even sometimes spreading their reign of terror to cities further inland. With their longboats they could go up rivers and back again quicker then you could call out a warning.
Vikings are dangerous.
Welcome to my ship. The land is in sight, so get ready to raid.