The Sino-Vietnamese War is rarely remembered or discussed today. But 40 years ago, the war appeared to herald a tectonic shift in regional and global politics and helped forge a close, more trusting relationship between the leader of the free world and the world’s largest autocracy. China’s 1979 invasion of Vietnam demonstrated that Beijing stood on the American side in the global Cold War—a message that President Jimmy Carter embraced. China may have been a brutal dictatorship, but the fact that it went to war against America’s erstwhile enemy, Vietnam, pointed to a commonality of interests between China and the United States.