This event, a result of the Berlin Conference of 1884–1885, which saw the imperial conquest of most of Africa, was a massive part of both African and European history. So why do many Americans not know much about this?

First, for a long time, world history was centered mostly on the West. Personally, my freshman-level world history class in 2002 was a survey on Western Europe. I remember learning about the French Revolution, World War I, World War II...and that's about it. My teacher was very passionate about European history, so that was our focus. I vaguely remember doing geography on all the world's countries, but that's it. As a history teacher now, I work hard to make sure the histories of all countries are represented, but I know that I'm in the minority.

I believe, like many of the previous answers, that the problem rests in rampant Eurocentrism. Americans and Westerners in general care more when it is closer to home. For example, when Ebola surged in 2015–2016 in West Africa, it made headlines in the United States when American aid workers came home potentially infectious. It stayed in the headlines for a few weeks; then the news dropped the story all together. Unfortunately, Ebola has continued to rage throughout Africa ever since, but our news doesn't cover it. Why? Because we are concerned with Eurocentric history, and if it doesn't directly impact the United States, it doesn't often make our news. This is also true of the history of genocides: the West was outraged at the Bosnian genocide when pictures that resembled the Holocaust were taken from Srebrenica in 1995. In response, NATO took control and put a swift end to hostilities. However, in 1994, the West knew about a genocide in Rwanda and purposefully pulled out all Europeans and left Rwandans to deal with their own tragedy.

Another reason that could account for why we don't learn about this genocide in the Belgian Congo is because when we learn about European activities in Africa, we tend to focus on the countries with the most colonies: Britain and France. The Congo was the only Belgian colony at this time, and it was privately owned by King Leopold II of Belgium, unlike the other colonies, which belonged to various European state. There was a lot of news that was covered up because of this. Thanks to photographers and news outlets, the massacres and atrocities were reported, and the international community shamed Leopold II into giving his colony to the country so it could be monitored better. Perhaps it is often overlooked because of this fact.

Regardless of the reasons, world history classes are starting to cover these atrocities. For example, in the New Jersey State Standards for World History, teachers cover the following standards:

• Analyze the impact of the policies of different European colonizers on indigenous societies, and explain the responses of these societies to imperialistic rule.
• Analyze the extent to which racism was both a cause and consequence of imperialism, and evaluate the impact of imperialism from multiple perspectives.
• Assess the impact of imperialism by comparing and contrasting the political boundaries of the world in 1815 and 1914.
• Analyze the motives for and methods by which European nations, Japan, and the United States expanded their imperialistic practices in Africa and Asia during this era, and evaluate the impact of these actions on their relations.

Americans have increasingly come to know about the atrocities committed by Europeans, mainly Belgians, in the Congo during this time period. However, the atrocities that were carried out in the Congo are not as well known as they should be for several reasons.

Americans have a tendency to focus more on the history and events in their own country and in Europe. They know little about Africa, its different people, or its history. They tend to be unable to distinguish between the histories of different African countries and tend to falsely assume that the African countries are similar when, in fact, they are quite different. Americans may also tend to pay more attention to the suffering of people in their own nation and in Europe. They tend to not focus on the suffering of people in other parts of the world, particularly in the developing word.

In addition, Americans tend to make the assumption that Africa has caused its own suffering by not modernizing. The reality is that imperialism, including the actions of the Belgians in the Congo, harmed Africa and affected its development, even today. It is difficult for people to understand that events that occurred over a century ago still affect parts of the world.

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.