"Majority-exploiter countries" is a term MIM uses to refer to countries that are at least 51% bourgeoisie in population. In that context we have to remember that the bourgeoisie includes not just capitalists but the petty-bourgeoisie.
Most of the people living in majority-exploiter countries are from imperialist countries. So this term zeroes in on something that MIM Thought specifically pertains too. However, the term also includes some small Arab countries that have enriched the majority of their populations through oil revenues now converted to assets in the West usually.
The list of majority-exploiter countries is part of the very definition of MIM. Included are Canada, Quebec, the United $tates, England, France, Belgium, Germany, Japan, Italy, Switzerland, Luxembourg, the Netherlands, Israel, Sweden and Denmark, though there may be more we have not studied in enough detail yet. This list is part of MIM's "Three Points" that are cardinal questions plus democratic centralism, the fourth cardinal question. We do not accept people as members who do not agree with this point.
The underlying economic basis for white and Japanese nationalism of both "left" and fascist sorts is that this list of countries is bought-off and benefits from nationalist class struggle against other countries. Exploitation carried out in national form is a root cause of war that threatens the species.
What MIM is saying is controversial among the petty-bourgeoisie and hence unpopular in the imperialist countries robbing the rest of the world. Politically, MIM refers to the defenders of exploitation as the "exploiter camp"--including both the self-labelled "left" and "fascist" parasites. In contrast, the politically allied people opposing exploitation are the "proletarian camp."