No they didn't. Some just wanted to take over stuff and said as much.

Indeed, and this should be stressed. The Mongols and the army of Alexander the Great are both examples of this. So are the various religion-fueled wars between Christian empires and Islamic empires. Hitler was another would-be conqueror who didn't make his ambitions much of a secret. Napoleon, too, was an invading conqueror; I don't know what arguments he made to justify his invasions of the rest of Europe, but he certainly acted like a conqueror.

We usually think of the Romans as conquerors, but they didn't think of themselves that way. In their writings, they almost always described their wars as defensive conflicts, much like the U.S. has.