I don't know whether you have any interest in the theoretical ideological and philosophical underpinnings of radical political Islam. Most people knew they wanted to fight fascism without reading Mein Kampf.
However, if you're interested, Fawaz A. Gerges writes in the Los Angeles Times about the three underlying documents which philosophically underpin the Islamic State, aka ISIS or ISIL. And, it is likely, provide rationale for most other violent Islamists.
These include The Management of Savagery, Introduction to the Jurisprudence of Jihad, and The Essentials of Making Ready (for jihad). This last one was written as a manual for Al Qaeda trainees.
Gerges characterizes each work briefly. I have no idea whether any of these are available in English translation, all likely were written in Arabic.
