(I only did the originals because the others would most likely win) Here are some ideas that might change your mind: Fallen- Are only here for their own survival. They are scavenging Earth because they lost their planet and are not one united force anymore. Hive- They are attacking us because they want to eliminate all light. They're trying to destroy the light so that their darkness can consume and control the entire universe. Vex- The Vex are trying to turn the planets in out solar system into machines for their own benefit. I don't know their intentions or if they are even known. Cabal- They're a highly militarized race and their main motive is to gain land. Considering they are kicked out of the empire during war, this is why they won't stop fighting us. Some say they are fighting against their will because of higher Cabal power.