What means "forcing an alliance?" You still sail under your flag, but as a protectorate of a larger nation? You have to obey what a captain from the conquering tells you? This definetaley needs a better explanation. Even if it will only come MAYBE to the game, I think plaers need to know what might happen.
I like the idea of regions, but if you make capitals open for capturing this will totally kill smaller nations playerbase. Forcing people to join something they don't want to join is not a good idea. It is just a game, don't go hyper-real.