Vikings controlled the countries they chose, they never dominated them.
Any country with sea access could be controlled by the vikings, so these countries tried to find ways to trade inland, which wasn't often successfull because of raiders and stuff.
So trading by sea was always the safest route for many, except when they were in a conflict with the vikings. Who simply waited for the slow galleys to try to hike down the coast, easy pickings. Call it Zone of Control or whatever, but they made fortunes of this and mostly without bloodshed. So soon countries and city-states paid ransom.
A Viking longship could hold 60-80 people, it could manouver in waterdepths of 4 feet, if lower the ship was so light, they could carry it over a sandbank or whatever.
It also had 2 sterns as it was built, so you just put in reverse in a second by flipping the rowers around, to go in the other direction.
Canute is said to have had over a 1000 of these ships at his hands, when he started his conquests. Think about that manpower! Not to even touch the tacticts they used when in war, like tying ships together, to keep a strong platform.
All this blabbling aside, I do not disagree with a new civ like Polynesia, anything new is a refreshment.

But I love Vikings.