I read that Muslim populations throughout the middle east in the beginning of the 20th century weren't as religious and extreme as they are today or even 20 years ago. What changes are largely responsible for the radicalization of the Muslim population in the ME in the 20th century?
What is extremism? Is violence? Is it extreme neo-Orthodox religious practice? Is it anti-Westernism? Is it a social vision where Islam is combined with the modern state?
You might be interested in two older answers of mine:
This focuses on modern Salafism (the most prominent Sunni neo-orthodoxy), modern Jihadism (with Qutb, which was initially primarily directed against domestic enemies like Nasser, and a vision to take over the state and run it Islamically), and the combination of those two threads (by Bin Laden, who also added a strong anti-Westernism--it took effort him to convince people to attack faraway America over the much closer secular "hypocrites" who ran Arab states). It doesn't cover a lot of stuff--I don't think there's a mention of the Iranian Revolution, for example, but it's really a short intellectual history of how we get to things like ISIS and al Qaeda, which tend to be what people think of when they think of "Islamic extremism".
The follow questions as the thread goes down get into a lot more about political Islam of all kinds, and away from terror.
This tries to take a somewhat broader view, but there's a lot going on because it really matters how you think of extremism. Make sure to at least read /u/DeSoulis's follow up, though the other comment thread is good as well.
Edit: if people have questions about this, they may also be curious about the Arab Spring. In another sub that doesn't have a twenty year rule, I went through what's happened to the Arab Spring from late 2010 until about nine months ago. I won't answers questions on that here because of the twenty year rule, but I thought people interested in this would also be interested in that:
As a related question, what led to the decline of Pan-Arab nationalism? Was it primarily the result of the Camp David Accords and the end of the Cold War, or was it more nuanced than that?