“... if any people ought to be allowed to consecrate their origins and refer them to a divine source, so great is the military glory of the Roman People that when they profess that their Father and the Father of their Founder was none other than Mars, the nations of the earth may well submit to this also with as good a grace as they submit to Rome's dominion.”
The military in ancient Rome is the foundation block of the Roman state, society and economy. As also said by Titus Flavius Josephus (Williamson, G. (tr.), Josephus, The Jewish War, 1959, p. 378
): The Roman people are "born ready armed”.
Rome existed and accomplish so much compared to the other ancient civilizations
because of its practice of war plunder economy. In the beginning when Rome expand from small village type city to dominating city state in the Apennine peninsula, the main reward for every Roman citizen – soldier were the plunders of war. If we observe the historical records, and time line we can see that as soon the Romans seize the practice of the plunder economy, their expanding wars, the main source of revenue dry out and the Roman Empire start to demise and eventually collapsed under the weight of huge cost to maintain its military, corruption and hyperinflation.
In conclusion, I do believe that the greed for plunder and military glory was the real driving force behind the Roman imperialism.