Answer: It is not realy a "split". That would imply two relatively large groups. The fact is that at least 85% of those who call themselves Muslim are all from one group. They are the people who follow the Qur'an and the example of Prophet Muhammad (peace be upon him). They are called 'sunni' Muslims, by some people. In fact, they are simply true Muslims.
The other 15% are all deviant sects that have corrupted the true, original teachings. Anyone who studies Islam can see how the other groups have changed the original message.
Shiites, Ahmadiyyah, Alawi, Ismaili, Druze are some names of deviant groups.
In fact, Muhammad said that there would be such deviants; and he condemned their teachings as leading away from God. He said that the only rightly-guided group would be the one that stuck to the Qur'an and to his example. We thank God that it is the clear majority.
For an understanding of why the Shiite sect developed, you can go to Wikipedia for a detailed explanation. For examples of how they have gone astray from the healthy and true religion, you can go to You Tube and search: Real Shiah Faces.
