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,
Ethnic groups in Burundi declared a presidential republic; however peace did not ensue as a result. Even after 1966, the subsequent dictatorial regimes of Michel Micombero (1966–76), Jean-Baptiste Bagaza (1976–87), and Pierre Buyoya (1987–93) were dominated by Tutsi elites which often consciously marginalized and discriminated against the Hutu majority. The first Hutu to become head of state was Melchior Ndadaye in 1993, although he was assassinated shortly after taking power. Ethnic violence peaked in 1972 when 100,000 people, mainly Hutu, were killed by the Tutsi regime in the Burundian Genocide. Twa have also been targeted, specifically in violence directed against the Tutsi with whom