Hutu Rwanda, this led to the "Social revolution" and Hutu violence against Tutsis. Tens of thousands of Tutsis were killed and many others fled to neighboring countries, such as Burundi, Uganda and expanding the Banyamulenge Tutsi ethnic group in the South Kivu region of the Belgian Congo. Later, exiled Tutsis from Burundi invaded Rwanda, prompting Rwanda to close its border with Burundi. In Burundi, a campaign of genocide was conducted against Hutu population in 1972, and an estimated 100,000 Hutus died. In 1993, Burundi's first democratically elected president, Melchior Ndadaye, who was Hutu, was believed to be assassinated by Tutsi officers,
Hutu Power and declared that any Hutu who did business with a Tutsi was a traitor to the Hutu people. The Commandments declared that "The Hutu should stop having mercy on the Tutsi" and referred to the Tutsis as "common Tutsi enemy". The Rwandan kingdom was traditionally ruled by a Tutsi mwami, or king; Historical evidence suggests that Hutu and Twa were included in government, although the Twa significantly less so than Hutu, who were more numerous. The Tutsi/Hutu divide has been referred to as a caste system. A Hutu could gain Tutsi status through marriage or through success. Tutsis, being primarily