To answer your question about what caused the flipping of roles, it’s a combination of the secularization of the West, which made it less dogmatic in its approach to those who didn’t subscribe to the dominant faith, and, at the same time, the rise and spread of the hard-line Salafi/Wahhabi branch of Islam, with its focus on literal interpretations of the Qu’ran. If you’re not familiar with this movement, you can read about the general outlines of it here. In more recent decades, the rise of Islamic terrorism was also influenced by the thought of Sayyid Qutb, whom you can read about in this comprehensive New York Times piece from 2003. (The New York Times today would likely not run a piece like this, because it would be too afraid of the P.C. police’s reaction to any implication that there is a problem within modern-day Islam.)