The Germans were worse.
The Herero and Namaqua Genocide in German South-West Africa (present-day Namibia) occurred between 1904 and 1907. Eighty percent of the Herero population and 50 percent of the Nama population were killed in a brutal scorched earth campaign led by German General Lothar von Trotha. Between 24,000 and 100,000 Herero perished along with 10,000 Nama.
I don't think the situation in Belgian Congo and South West Africa were directly comparable, because in one case it was the slave like labour, profit orientation, corruption and brutality of all groups associated. Including the locals which sometimes just abused a system and the upper colonial ranks just looked away or were not able to control it. Whereas in the later case of South West Africa, it was a brutal guerilla war. The Germans simply cut off the rebels from water and food, since they were not able to control them otherwise in the huge, hostile terrain. The rebels started with extremely brutal acts against the local Europeans, men, women and children, truly horrible acts, which incited brutality on both sides naturally. So what they did was not profit oriented, it was not simply brutal and numb, it was the reaction to a specific situation. That way they could safe their own lifes, shorten the war and pacify the region. Guerilla wars of that kind, especially if they start like that, with the extremely inhumane and most brutal acts against the local Europeans, are always nasty, that's just as it is. Such wars can be led differently, but only if you want to lose more of your own civilians, soldiers and probably the whole war. it was not a deliberate genocidal act, because otherwise these tribes would no longer exist. We now have this attitude of "the civilised side" is always wrong, even if it just retaliates, whereas the "suppressed" are always right, even if they are more brutal in their methods (Marxist interpretation of reality).
The Herero started their attacks without provocation, in a situation in which the local civilian European settlers were completely unprotected. You can read up about it in the Wikipedia article:
The Herero revolted in early 1904, killing between 123 and 150 German settlers, as well as seven
Boers and three women
A Herero warrior interviewed by German authorities in 1895 had described his people's traditional way of dealing with suspected
cattle rustlers, a treatment which, during the uprising, was regularly extended to German soldiers and civilians, "
We came across a few Khoisan whom of course we killed. I myself helped to kill one of them. First we cut off his ears, saying, 'You will never hear Herero cattle lowing.' Then we cut off his nose, saying, 'Never again shall you smell Herero cattle.' And then we cut off his lips, saying, 'You shall never again taste Herero cattle.' And finally we cut his throat."
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According to Robert Gaudi, "Leutwein knew that the wrath of the German Empire was about to fall on them and hoped to soften the blow. He sent desperate messages to Chief Samuel Maherero in hopes of negotiating an end to the war. In this, Leutwein acted on his own, heedless of the prevailing mood in Germany, which called for bloody revenge."
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The Hereros, however, were emboldened by their success and had come to believe that, "the Germans were too cowardly to fight in the open," and rejected Leutwein's offers of peace
https://en.wikipedia.org/wiki/Herero_and_Namaqua_genocide
So the whole story had two aspects: Military necessity and retaliation. Its not like the Germans were more brutal than the locals, not at all. The many men, even those which killed and tortured themselves, which could be interviewed afterwards, speak for themselves and the will of the Germans for a true "genocide".
Looking at what Caesar did in his campaign, he is more comparable to what the Germans did in Africa, because he too oftentimes offered friendly terms at first, and only when leaders and tribes betrayed him or acted very gruesome against his own people, he changed the pace and started to eliminate the resistance. Like in one case, he offered one tribe peace the first time, then they rebelled, but were subdued, and again got a favourable peace. But the third time, when they massacred the local Romans in a most brutal way and were stubborn, until they had no choice but to capitulate a third time, after Caeasr forces lost many men, material and time, they were all slaughtered or sold into slavery as a whole, to make an example of it for all of Gallia. One could question what he did, but at least going by the sources, that seems to be a reasonable approach.
That's also why some Gallic tribes even profited from the Roman conquest, while others were practically annihilated, sometimes, or even most of the time, after having breaking off and rebelling against the Romans the 2nd, 3rd or even 4th time.
Of course one could question the presence of colonial or any conquering force in the first place, but that's not the point, because all people did that at different times and circumstances. Its about how you treat subdued people "if they behave" and how you treat them "if they don't" and you simply have to protect your own soldiers and civilians. Like in various uprisings, also against the Romans, there were most brutal acts against Romans, soldiers and civilians. One prominent example is Boudiccas rebellion, which tortured and mutiliated tens of thousands of Roman men, women and children to death.
For me it makes a big difference, probably the biggest, talking about humanity and decency, whether you just kill enemies, or torture them to death in the most gruesome ways and let them suffer for a prolonged period of time, probably even with a sadistic pleasure. Men like Casear could be brutal and goal-oriented, but they were rarely if ever gruesome and sadistic. Which I think is a good quality, especially in his time, in the social and moral context he lived in.
