Let's say, hypothetically, that it's the second century AD. The Roman Empire, for some reason or another, declares war on the Gupta Empire in India, and sends all of the legionaries and Auxiliaries she can muster. Meanwhile, the Han Dynasty in China tries to capitalize on this moment and declares war on both of them. We'll say for the sake of arguement that the sheer distance between the 3 regional powers is not a factor. Who do you think would emerge victorious?