Conflicts between sects is not unknown in other religions too.
For example look at the European wars between Christian sects just prior to the Enlightenment.
I think the key thing here is that Islamic countries for one reason or another never went through a similar transition towards rationalism and individualism. They are still ruled by a way of thought that western culture started abandoning 350 years ago.
I hope we don't get dragged back that way. Fundamentalism is ultimately I think the greatest enemy of human progress.