The constant by Kazao

I've been thinking about the idea of a war between Jacob and the MIB. From the moment we saw them in the flashback it seemed like they had just a major disagreement on whatever it is they are talking about. My theory is Jacob and the MIB have gone through countless cycles of time. They have seen it end every time and it does not end the way Jacob wants it to end. They seem to be godlike people. I believe that just like Desmond became special when he blew the hatch Jacob and the MIB became special the first time they repeated the cycle.
The reason they couldn't kill each other was because they were each others constants. I don't have a theory on the negative repercussions of Jacob's death but it I believe MIB killed him to end the constant loops of time.