That depends whether you ask a Shia or Sunni. As I understand it, Islam started fracturing on day 1 due to debate about the true succession of Muhamed. I mean, consider all the various fractions of Christianity. The big one, Orthodox vs. Roman Catholic. Catholic vs. Protestant, and all the variations of Protestantism (and Catholicism, Orthodox). Its the nature of religion and more broadly, the nature of art and reading IMO. Sunni and Shia are just as fregmented I'm sure. ISIS appears to be another sub-fragment of Sunni, localized to the Syrian-Iraqi situation. With a fair number of foreign extremists and psychos thrown in for good measure. But ISIS's interpretation of Islam is not more or less valid than any other.