What doctrial differences separate Shite and Sunni Muslins?

Shiah belive that Prophet Mohammad appoited his 12 Imams by the order of GOD ,to be Muslims leaders after him ,till the end of the world and believe that Jesus Christ, on his second return, will meet with Imam Mahdi, the twelth Imam and together will established a world government that will bring real peace and justice ,before the end of time.

The Sunni did not believe in this and confirm that Prophet Muhammad did not appoint his suceesor before his demised.

By the way Jesus apointted his twelve disciples by the commandment of GOD,before he was raised up alive to high heaven ,then Prophet Mohammad practice the same traditional of GOD by appointing 12 Imams ,one after the other ,from the first Imam Ali bin Abi Taulib till Imam Mahdi ,the twelfth Imam or the awaiting Imam of the last generation of mankind.

the 'big issue' is over who gets to claim being the chosen spiritual heir to Mohammed.

After that comes whose teachings are the more important in Islam -- the Shi'a heirs' or the Sunni heirs'. [If the big one is settled, then the followers of that branch and their teachings get to lord it over the other one.]