Since the escalation of tensions with China in the South China Sea in recent years, the Sino-Vietnamese war has begun receiving renewed media attention. This paper first traces back the incidents that led China and Vietnam to a short yet devastating war launched by China in 1979. The dynamics and roots behind the war came from Beijing internal political reasons rather than what Deng Xiaoping accused “Vietnam’s incursions into China-friendly Kampuchea”. In this respect, the developments during and post war times have been identified and analyzed to respond to the unsettled questions: who was the "true aggressor," China or Vietnam? and who must be responsible for dozens of thousands dead and injured in the 27-day war. The paper concludes with a discussion of that China and Vietnam should both pigeon-hole their tragic past and seriously study the dear lessons drawn from the 1979 war to avoid the same mistakes in the future.