Sythbane Squadron charter member
I was playing Halo 2 not long ago, and I noticed some modern day traits of evil in the Covenant. They are like two evil entities that exist in this world: the Nazis, and the terrorists of the middle east.
The three "prophets," which are basically powerful alien preachers, are like the Axis, the Prophet of Truth being a Hitler figure. He uses false promises of glory and salvation in the "Great Journey" to motivate the Covenant to help him activate the rings. The rings, however, are weapons capable of wiping out life in a galactic scale.
The honor-guard elites are fanatically devoted to serving the prophets as the SS troops served Hitler. There is a point in the game when one of the prophets is displeased with an elite, and he says, "You let the humans land on the sacred rings and desecrate it with their filthy footsteps." This is sort of like the Nazi view toward the Jews. The Covenant wants to wipe out the humans as the Nazis wanted to wipe out the Jews.
There is another point in the game where the Prophet of Truth says, "The council planned to have you hung by your entrails and your corpse paraded through the city." This is like what the Romans would do after a victory -- parade their fallen enemy through the city in a chair to disrespect him.
The way the Covenant are like terrorists is like when the Arbiter character is introduced. A Covenant Arbiter is a disgraced Covenant that has failed in some way but is given another chance for "glory" by being sent on a suicide mission. This is like the suicide bombers who are told they will be rewarded for blowing themselves up. Their other trait is their fanatical dedication to killing "infidels," which in this case are humans.