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Today, half a century after the Sino-Indian War, the geopolitical rivalry between the world’s two main demographic titans is again sharpening, as new disputes deepen old rifts. Booming bilateral trade has failed to subdue their rivalry and military tensions, and China has largely frittered away the political gains of its long-ago victory. But the war’s continuing significance extends far beyond China and India. By baring key elements of Beijing’s strategic doctrine, it offers important lessons, not only to China’s neighbors but also to the U.S. military. Here are just six of the principles the People’s Republic of China relied on in attacking India—and will undoubtedly use again in the future.