That war will end when there are no infidels alive in the world or when there are no- zero- Moslems. If it is the first case then the intra Moslem war will continue until the end of humanity.
You are right about that.
The sunni/shiite divide is but one of many.
Yes, when people have been taught that it makes sense to kill their daughter for dishonoring the family if she is raped they have been rendered criminally insane and they will always find someone to attack. They are unable to think rationally, some will say this applies to religion in general but I say it applies only to those who have been taught Islam from birth. Islam is intellectual poison and it was designed to be exactly that. In the days when the Roman Catholic church executed people for witchcraft and heresy it was little better if any than Islam but Islam has not changed for the better in such respect, followers of Islam still think they have a command from their creator to destroy all who believe differently. Such thinking is a formula for unending war and destruction which can only stop when there are no more humans left on Earth.