differences between elijah and xavier

I think the tension between the two boys is one of contrasting and colliding cultures. While Xavier rejects the English speaking vernacular, Elijah seems quite content even welcoming his name change from Weesagechak to Whickeyjack to make it easier for English speakers to pronounce his name. Both evolve into two very different people. While Xavier has no thirst for the war or killing, Elijah is sick with the need for destruction. He is addicted to morphine and killing Germans. He scalps his kills as part of a twisted identity connection with his roots. Quite simply, Elijah has gone insane and Xavier can no longer handle the madness. He feels must put a stop to Elijah's demons, he must end his (Elijah's) life,

“You have gone mad. There is no coming back from where you’ve travelled.” I press down harder. Elijah’s eyes shine with tears. His face grows a dark red. He tries to whisper words to me but I know I cannot allow Elijah to speak them. I must finish this. I have become what you are Niska."