Thanks, I had never heard about that and just had a quick read on it. I can see where it links with the "promotion" of the Tutsi in Rwanda.
Though I also venture that the colonial projects were pragmatically self-serving, first and foremost, and only adopted those ideologies that could be used. And then in turn promoted them. In the 19th century states were not particularly wealthy and both colonial companies and "state-managed" colonies had to make do and turn a profit. That meant organizing the exploitation of the african populations, as we all know, because europeans would not migrate there in large numbers. Colonial governments would do anything that was expedient to extract the maximum of traceable wealth from those populations, with the smaller costs. Infrastructure was limited to ports in the coast or rivers, those were fixed costs for each territory. The variable costs were the military, the cost of repression. This the european colonial governments would go along with whatever structures were already in place and willing to cooperate in that extraction of valuable goods.
Did the belgians and the french actually went to the trouble of installing a group over another, with the military costs necessary for that? Or did they exploit structures that was already in place and nudged them along?
Not sure if you mean permanent re-location, yet the belgian Congo did use other africans (from outside Congo) as the Askari (lower soldiers), exactly because those other africans would have less issue with chopping hands of the congolese natives. Besides, this has been the reason why mercenary troops were so popular from ancient times: they can only be loyal to their ruler, and thus they stand or fall with the ruler and will destroy the natives if asked.