New Imperialism and Old Imperialism are terms used in history.
They're part of the current historical fashion. So what? People end up reinterpreting history each new generation anyway. I'll stick to my view that those terms are inappropriate.
And Africa was in fact politically subjugated, unlike some of the Asian countries.
If you hunt for exceptions you'll find them also Ethiopia, Liberia. Each place's history is unique.
There are other reasons why settlement was not done significantly in Africa despite the pretty successful conquests, and they have been pointed out in this thread.
Some of those (the "Jared view") are nor a real explanation. There were no unsurmountable natural barriers to european expansion there, nor human barriers (opposition). It was a matter of resources and priorities (and chance, also).
Democracies were fine with subjugating the natives and depriving them of rights since they were considered 'uncivilized'. And it's not like each democracy cared much about people outside of itself anyway.
No, that's too simplistic a view, for such an important subject. The issue of representation is
old. Medieval european societies had their forms of representation already, whether the english parliament, the french provincial parliaments, the iberian cortes, the polish sejm, etc.
Who was represented in these changed, of course, and most started with the nobility and evolved into incorporating other elements (with some drifts on the opposite direction). The american colonists of england gave it enough importance to present it (lack of representation) as the main cause of their declaration of independence.
There was no tradition of depriving natives of rights because they were "uncivilized". There was a tradition of
distributing rights unevenly, which favored a small elite - even in 18th century england (once again, the denunciations of the "corrupt" english parliament... first by english politicians and the taken up by the american colonists). The issue of the natives' rights was indeed discussed during the 16th century (the polemic in spain about whether native americans had souls and could be enslaved...) which ended with natives being officially recognized as citizens. Unfortunately for them, citizens on the lowest level, the one which hardly got represented, anywhere. But it wasn't because they were "natives", it was because they were "plebians".
Even during the earlier europena colonization colonial cities did sent representatives to their country's assemblies, or at least that was the case with several spanish and portuguese colonial cities. Only two changes, combined, would make this practice uncomfortable to power centers: when the colonies became bigger that the "mother country", and when the idea of political equality took hold. These were the cause of the separation of the remaining european colonies (from Spain and Portugal), as liberalism took hold. The power elites in the capitals would simply not accept that they might lose control of state affairs to the elites of some far away territory.
The new wave of territorial imperialism, in Africa and Asia, had to take these changes into account. And it was
then, as a defensive reaction against the potential "electoral thread" of natives within a liberal democratic regime, that new racial theories ("scientifically validated", of course), were put forth, now seeking to characterize natives as hopelessly uncivilized and therefore to be excluded from the political process altogether.
In fact I believe that one of the two main reasons europeans governments at first opposed private efforts at territorial imperialism was precisely a fear of getting entangled in that political problem. The second reason was, obviously, the cost of those colonial adventures for the public finances (especially as the profits tended to be private).