Hutu as was the person constitutionally entitled to succeed him. This sparked a genocide in Burundi between Hutu political structures and the Tutsi military, in which an estimated 500,000 Burundians died. There were many mass killings of Tutsis and moderate Hutus; these events were deemed genocide by the United Nations International Commission of Inquiry for Burundi. While Tutsi remained in control of Burundi, the conflict resulted in genocide in Rwanda as well. A Tutsi rebel group, the Rwandan Patriotic Front, invaded Rwanda from Uganda, which started a civil war against Rwanda's Hutu government in 1990. A peace agreement was signed, but
Hutu of Rwandan national unity, but has been criticized as an attempt at historical revisionism. Still others suggest that the two groups are related but not identical, and that differences between them were exacerbated by Europeans, or by a gradual, natural split, as those who owned cattle became known as Tutsi and those who did not became Hutu. Mahmood Mamdani states that the Belgian colonial power designated people as Tutsi or Hutu on the basis of cattle ownership, physical measurements and church records. There is an ongoing debate as to whether the Hutu and Tutsi are really separate groups or not;