What would the world be like today if everyone had stayed at home since day 1?
No conquering, no invasions ......
Well, for one, society would have been held back.
Economics is really a broader field than one would think. Its principles extend everywhere. One economic theory, capitalism, has as one of its principles that good money drives out bad; that through competition, inefficient producers are driven out of business in favor of efficient ones.
Similarly, though conquest can be seen as an evil, it's also true that inefficient societies are generally the ones driven from existence. When inefficient societies fail, better ones take their place, hence we have Western Civilization, which has given us concepts like individual rights, and has produced modern computers, machines that fly through the air, and space travel.
Had no conquest occurred, I doubt wondrous things like those would have ever been invented.