Two of the three wars between the Chinese and nomadic peoples indirectly led to the fall of the Roman Empire, while the last one largely saved Europe.

Foreword: Human history, in essence, is a process of barbarism constantly impacting civilization. Whether in the East or the West, barbarians (nomadic peoples) have always challenged civilization (e.g., the Roman Empire, Chinese dynasties, India, Persia, etc.). If discuss which three nomadic people