Both Sunni and Shia Islam are in fact fairly tolerant, as can be seen in Sunni Muslim Iraq which previously (prior to the Iraqi War) not only tolerated but took an interest in other religions.
Professor Valentina Colombo, who teaches Geopolitics of the Islamic World at the European University in Rome and Dr. Mark Altaweel, a Lecturer in Near Eastern Archaeology at the Institute of Archaeology, University College London enlighten us on these issues.
It would seem that destruction of religious and cultural artifacts by hardline ISIS militants serves two purposes: to raise money on the resale of those objects which they do not destroy, and to raise public awareness to the ISIS cause. By destroying history ISIS is saying that nothing but the present exists, and the present is ISIS. ISIS has successfully drawn the world’s press into their own court. As Professor Colombo points out, ISIS was born as a public relations organization out of Al-Qaeda, and only 14% of the world Muslims speak Arabic.
Because Islam has no central authority, it is difficult to encourage Islamic groups themselves to settle the problem of extremism, although this may be the only lasting solution.