I started wondering about this question after the recent attacks in London. I know it is a delicate topic, but I think its worth asking because, while we often hear about terror attacks, only rarely do people talk about their causes. So, again, what caused the birth of Islamic Terrorism?
The answer I will provide is simplistic, as books have been written on this topic. I have an MDiv, and my thesis was on the perception of religious movements and what causes the public perception of cults. I looked into Islam to a great degree, and will be providing an answer with theological roots: there is more than one way to address Islamic terrorism, however.
Islamic Terrorism is not without precedent. Since the Prophet Muhammad began his recitations, the concept of war was not foreign to Muslims. War was a necessity as they moved throughout Arabia and Northern Africa, expanding beyond Mecca and Medina. While Islam primarily grew through trade routes, war (or force) enabled Mohammed to consolidate power.
You have likely heard of the term Jihad. You likely have misconceptions about it. The Quran and Hadith, two guiding sources for Islam, provide context for Jihad. There are two "types" of Jihad, which literally translates to struggle- the greater Jihad, where one struggles with their own sins; and the lesser Jihad, where on struggles against others with force to protect Islam. Jihad is the foundation for schools of thought in Islam, and the many sects that have sprouted from Muhammad's first followers.
However, war and force is certainly contentious. While I am certainly no apologetic, I would like to stress that the perception of Muslims on this topic is mostly unfair. When you hear of Muslim support for "Jihad", to the Muslim Jihad is not only war. It is debate, it is prayer, it is inner reflection and meditation. Yet to some, Islamic Terrorism is Jihad.
The foundation for 21st century Islamic terror is likely rooted in many areas. Colonialism, economic exploitation, orthodox Islamic interpretations (Wahhabism and Qutbism), and misguided fervor are all variables in this complex question. I will highlight the story of Sayid Qutb, 20th century Islamic theologian and author of Milestones, to provide one example of how complex the roots of terrorism are.
Sayid Qutb is the academic founder of offensive Jihad. While the act of wars abroad in the name of Islam existed before him (think the wars in Middle Asia circa 1400's), Qutb provided much needed theology behind Jihad in the modern nation state context. Egyptian, he traveled to England for education and was disgusted by the "decadence and debauchery" he encountered. Returning to his homeland, he met with rather extreme religious leaders: so extreme he found himself in jail for treason.
Though he would be released, his writings were inflamed due to his treatment by authorities. Founding Qutbism, his Wahbist based ideology is ultra-orthodox, promoting total disloyalty to secular governments and encouraging any Jihadist attacks against secular governments, or the people who compose them. Boko Haram in Africa is one group which uses this ideology, whose founder was a former student of Qutb.
While not all Islamic terrorist groups are Qutbic, this story provides a loose model for other organizations. Islamic terrorism in modernity stems from early theological precedents, adapted by the disenfranchised who see corruption in the world. Because of the early acceptance of war in Islamic culture, these ideas have been interpreted liberally in this day and age.
Past answers to similar questions about Islamic terrorism.