Preemption
This doctrine is centered around the attempt to repel or defeat a perceived imminent offensive or invasion. The aim is to gain a strategic advantage in an impending (allegedly unavoidable) conflict shortly before it materializes into a crisis. Its principles include unilateralism and the use of preventative war.
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.
