As the Netherlands, I'm on a quest for world domination. My current enemies are Great Britain, Spain and Portugal, and I would love to take over their colonies. In my last war against GB, I annexed all of British Columbia, thinking it would immediately trigger into forming Dutch Columbia. But it didn't. Instead I was left hanging with 175% overextension. (Although I didn't get any rebels or events. Also, I don't think I should get overextension for overseas provinces. Anyone know what's going on here?) However, once one of my nearby colonies became self-sustaining, this triggered the entire area into forming Dutch Columbia.
So if I want to take over enemy colonial nations, I should just annex them, ignore the overextension, and then settle nearby. Once the colony finishes, the entire region will form a new colonial nation. However, many of the colonial nations I want to conquer don't have free land nearby (or in some cases, I'm unsure as to whether the nearby land falls under the same colonial region). How do I get these colonies to trigger?