So, let's say the US closes it's borders after the Civil war, perhaps because of UK and French support of the Confederation, leading to a longer, bitterer war, and xenophobia towards those god-damned Europeans. No point in defeating them if you're gonna let them all move in the next year, right?
Anyway, could this direct surplus populations towards Africa enough to lead to large-scale settlements across the continent? I'm thinking draining of marshes, clearing jungles, eventual industiralization, a treatment of the Africans similiar to that the Indians faced in the US (land theft, deportations, reservations, large-scale killing, diseases etc) leading to a pre-dominantly white or at least White-dominated sub-Saharan Africa. Throw in an east-African Israel to that.
Is this plausible in any way?