The Sino-Soviet split had important ramifications in Southeast Asia. Despite having received substantial aid from China during their long wars, the Vietnamese communists aligned themselves with the Soviet Union against China. The Khmer Rouge had taken control of Cambodia in 1975 and became one of the most brutal regimes in world history. The newly unified Vietnam and the Khmer regime had poor relations from the outset as the Khmer Rouge began massacring ethnic Vietnamese in Cambodia, and then launched raiding parties into Vietnam. The Khmer Rouge allied itself with China, but this was not enough to prevent the Vietnamese from invading them and destroying the regime in 1979. While unable to save their Cambodian allies, the Chinese did respond to the Vietnamese by invading the north of Vietnam on a punitive expedition later in that year. After a few months of heavy fighting and casualties on both sides, the Chinese announced the operation was complete and withdrew, ending the fighting.