
Functionally, barbarians are early-game threats to the player, minor enemies to pester budding civilizations or, alternatively, target practice for those new to world domination. Civ 5's manual calls barbarians "fiendish." It describes them as "roving bands of villains who hate civilization and everything that goes with it." Does this sound like the divisive binary rhetoric espoused by George W. Bush to you, when he stated of terrorists that they "hate our freedoms?" It does to me.
Barbarians are civilization's antithesis, malevolent forces of chaos with no rational for their actions. The game periodically generates barbarian forces in spaces players cannot see - they literally spawn from darkness. Also, unlike other civilizations and city-states, players cannot interact diplomatically with barbarians, they only exist to undermine progress.
Barbarian spawn points are called encampments, which seems to imply they are temporary fixtures of nomadic peoples, a far cry from the settled inhabitants of civilizations. Strangely though, barbarians are also designed to maintain pace with the players, allowing them to spawn a military unit equal to those of the most technologically advanced civilization. This means these backwards barbarians can spawn tanks and bomber planes, and will continue to do so "until the entire world is civilized."

What of the barbarous people? Are they simply eradicated, dispersed into the wind? Or does my civilization teach them the error of their ways? Do the Romans give them a bath and a philosophy teacher and thus "civilize" them? While I respond to the procedural imperative of progress, expanding my borders and advancing technology, I can not help but feel confronted by the rhetoric of backwardness and savagery. The Roman empire is following a linear path towards development and growth, one with no room for the barbarous. Forgive them, for it is the only path they know.