Rwandan history is construed based on your political bent. If you are pro-Hutu, you have one dispensation and if you are pro-Tutsi, you have another. The divisions have largely to do with whether Hutu and Tutsi signify two distinct peoples and, relatedly, if the Tutsi are a foreign people.
The pro-Tutsi line of reasoning sees no distinction between Hutu and Tutsi. This division was created by the Belgian colonists based on social class. Rich people were designated Tutsi, while poor were deemed Hutu.
The pro-Hutu stance is that the Tutsi arrived to the region from elsewhere. This argument follows the colonial racialization of Hutu and Tutsi. As Mamdani asserts, the Belgians did not create the Hutu and the Tutsi, but they did racialize them. The colonists viewed the Tutsi as members of a superior race. The pro-Hutu stance believes that the Tutsi are a Hamitic people and thus, nonindigenous to the region.
The stereotypes of both groups involve the belief that the Tutsi have historically been pastoralists while the Hutu have been agriculturalists. This reinforces the belief that the Tutsi migrated from elsewhere. It also perpetuates the idea that the Tutsi constitute a higher social class, because cows were associated with wealth. But the stereotypes of the Tutsi pastoralist and the Hutu agriculturalist are muddied by history. The idea of the Hutu-Tutsi division on the basis of social class flatly ignores the existence of poor Tutsi.
These debates have had tragic consequences for the people of Rwanda. Hutu Power argued in the early 1990s that the Tutsi were foreigners and posed a threat to the indigenous Hutu. This fear helped to instigate the genocide perpetrated against the Tutsi in 1994. After the genocide, when the Tutsi-led RPF took power, the leadership argued that there was no division, going so far as to outlaw the terms. That has served to legitimize their ethnic minority rule. It also gives persecuted Hutu no recourse to protest their treatment because the source of their oppression is legally nonexistent.
Hiernaux argues that the Tutsi are “elongated Africans” from East Africa that have adapted to the life of desert nomads. This line of reasoning shows that while Tutsi and Hutu are different people, the Tutsi do not constitute a foreign race. Mamdani adds that Tutsi migration likely did not occur in one invasion, but happened gradually.
The pro-Hutu and pro-Tutsi beliefs as to their origins need to be considered critically and tested against history. (more on Rwanda at HQT-IE)