I'm not going to write out all the history so here is a beautiful article about the history of the Kharijis.
http://lostislamichistory.com/who-were-the-kharijis/
In short it talks about the rise of a group called the Kharijis who disagreed with the current caliph who was Ali.
They ended up having very twisted views of Islam and committed horrible atrocities all stemming from their view that Ali had made a mistake in his rule. Ali making a mistake (from their view) eventually warped into the belief that all rulers should be free from sin, this warped into the idea that people who sin (mainly focused on Ali) are disbelievers, this warped into an idea that they should kill all who sin. But clearly they kept making up ideas to fit with their political agenda which was to kill Ali (which they ended up doing) and all those who supported him, by the time Ali was dead the movement kept moving and caused much destruction before it eventually dies out.
The main people who ended up following and joining with the Kharijis were uneducated youths who didn't really know much about Islam themselves.
Why knowing this history is important is because all this is extremely similar to ISIS today. ISIS formed by taking grievances to the extreme, just like with the Kharijis. ISIS twists Islamic teachings for their own political purposes, just like the Kharijis. And ISIS mainly recruits from those who know little about Islam but feel they need to make up for it, just like the Kharijis. In order to stop ISIS we need to learn from our past.