Because The Maurya Empire in India used a combination of political sabotage, religious conversion, and military conquest to expand its rule. The Romans, although a militaristic society, did not generally set out to conquer territory. But, they did get involved in many wars.
I hope that helps.
Huns, Vandals and Visigoth :)
There are three main reasons for European Exploration. Them being for the sake of their economy, religion and glory. They wanted to improve their economy for instance by acquiring more spices, gold, and better and faster trading routes. Also, they really believed in the need to spread their religion, Christianity.