Invasions and expansions
The romans conquered many places, for example: France, Africa, Germany, Balkans Spain, and the Middle East. They also took the people of these countries as slaves or maids. Romans were experts in trading that’s when they began to think and say “oh, why don’t we stop conquering the land and instead go and start a trading business with them” so in that way it was a win win for both sides the romans would get natural resources from that country and the other would get the same but also it wouldn’t have to loose it’s country either and most of all there was peace in the land.