In 1978, Chinese troops went into Vietnam to “teach Hanoi a lesson”, completing a full circle of bilateral relations that went from almost complete integration to enmity. China was putting pressure on Vietnam, which itself had invaded Cambodia and forcibly changed the regime there.
China’s move, taken in agreement with and with the full knowledge of the Americans, despite failure in the field – Vietnam resisted valiantly and taught China a lesson – helped to bolster Beijing-Washington relations. Yet a quarter of a century later, the memory of that invasion still haunts relations between China and Vietnam.