Between 1880 and 1920, the population of the Congo was slashed in half: some ten million people were victims of murder, starvation, exhaustion, exposure, disease and a plummeting birth rate. Why do you think this massive carnage has remained virtually unknown in the United States and Europe?
There is, of course, no way to know this for sure, but we can make some conjectures.
First of all, we have to consider the time at which this took place. During the late 1800s and early 1900s, there was not much American interest in things like human rights, particularly in faraway places. For example, it is not as if the Armenian Genocide in World War I got much attention either.
Second, we have to consider where this happened. The Congo was not a place that was particularly well-known in the United States. It is possible that such a massacre in Canada or Western Europe would have caught people’s attention, but in Africa, it was much less likely to be noticed.
Finally, we have to consider that it may be partly due to racial issues. It is possible to argue that Americans are less likely to care about what happens to people who are not Western Europeans or their descendants. It is possible to argue that Americans are less interested in the plights of people who seem to be fairly primitive in the first place.
Added to all of this is the fact that it is likely very difficult to document exactly what happened this long after the fact. All of these factors are likely reasons for the fact that this part of history is not well-known.