The Cambodian genocide occurred from 1975-1979 under the Khmer Rouge regime led by Pol Pot. An estimated 2 million Cambodians were killed. In 1979, Vietnam invaded Cambodia and overthrew the Khmer Rouge due to their paranoid attacks against Vietnam and alignment with China. The invasion was driven by Vietnam's desire to become the regional hegemon as well as retaliate against the Khmer Rouge attacks, but was also influenced by the geopolitical tensions of the Cold War between Soviet-aligned Vietnam and China-aligned Cambodia. The United States initially sided with the Khmer Rouge against Vietnam due to broader Cold War dynamics.