Why many countries want to conquer the world?

For example, when Spain discover América and kills all the natives and build and empire wich is made to work and colect resources like gold for the Spaniards. Or maybe some country looking for resources in South America, and it kills some presidents, bribe some gobernors, infuse crime and violence into the society... show more For example, when Spain discover América and kills all the natives and build and empire wich is made to work and colect resources like gold for the Spaniards.
Or maybe some country looking for resources in South America, and it kills some presidents, bribe some gobernors, infuse crime and violence into the society to make people dumb and easy to control.
I mean that was ok in the Roman Empire, cause there were though times to survive and stuff, but this days, really, what's the big need for that?
3 answers 3