Sunni vs. Shiite

I've often wondered about the differences between Sunnis and Shiites, and why the conflict and confrontations occur between the two. After researching the issue, several truths became apparent. Sunnis and Shiites both follow the teachings of the prophet Muhammed, and are practitioners of Islam.
The main argument between the two sects seems to be the murder of Ali after the death of the prophet Muhammed, and the dispossession of the Caliphate from those who are believed to be the rightful heirs. Despite their differences, the two sects have lived together in peace for the majority of 13 centuries.
There are differences, but what religion doesn't have them? Catholics and Protestants have been fighting since before history, most notably in "The Troubles" of Ireland. Many Schisms have occured over the course of time: The Protestant Revolution, being one of them. But perhaps no other sect, or sects have been subject to outside influence like the Sunnis and Shiites. It is a volotile situation, and one that has been taken advantage of by political adversaries. Divide and conquer. Take a look at present day Iraq, Iran, and Pakistan. All of these countries are populated with Muslims, and all have experienced or are experiencing foreign prescence and occupation. A nation divided against itself will fall, which is a lesson the United States has learned, and taken advantage of.
Reconciliation , or at least peaceful coexistance of these two sects of Islam could be possible, if outside forces and influences didn't seek to drive them apart.