There are so many parts of Westeros we did not see in the first 4 seasons of the show.

There are way more Bolton loyalists than I imagined.  I wonder if they're loyal in the same sense that Reak is loyal.

Yes, the North always has had lose coalitions based on coercion and convenience.

It is easy to break those bonds, too.

Just in the time of the show we've seen The North defect from Kings Landing to hail Robb Stark.

And then defect from Robb Stark to hail the Boltons. 

Defecting from the Boltons won't be hard.

But to whom will they become loyal next? Stannis? Jon Snow? Sansa and Littlefinger?

It remains to be seen.