I was wondering, having watched an interview with Maajid Nawaz, where did the modern jihadi movement come from. Not just causes, but also who were the intellectual foundations of the movement and how they justified it.
A few weeks ago I covered a question similar in scope that might help answer your question. It's in two parts, but the second part here specifically talks about the roots of jihadism. (The first part might also be helpful, since it discusses European colonialism's role in setting the stage for these movements in the 20th century.)