Tales and Chronicles
Jewel of the North, formerly know as vincegetorix
You mention "colonialism" as a time period frame, which makes me ask the question: are they actually going to be colonies? Is there an Old World power these folks still must answer to? What is the relationship between the two? Mutually beneficial? Extractive? Contentious?
I'm not sure.
I love the idea from Symbaroum, where whole kingdoms moved to the new world (across the maintains in that specific case). So maybe 1 or 2 kingdoms from an ancient world who fell beneath the waves?
I have in mind of having ''colonies'' but no colonial powers, so no big empires try to steal stuff from our continent.