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,
Rwandan genocide or simply having a "Tutsi appearance". The RPF was making slow but steady gains in the north and east of the country, ending the killings in each area occupied. The genocide was effectively ended during April in areas of Ruhengeri, Byumba, Kibungo and Kigali provinces. The killings ceased during April in the "akazu" heartlands of western Ruhengeri and Gisenyi, as almost every Tutsi had been eliminated. Large numbers of Hutu in the RPF conquered areas fled, fearing retribution for the genocide; 500,000 Kibungo residents walked over the bridge at Rusumo Falls, into Tanzania, in a few days at the end