Islam: More Violent? I find the idea of radical terrorism being Islamic rather ironic, as the justification for it was actually a Christina doctrine first.
Augustine's Doctrine of Secular Law as a Danger to Faith
In "City of God" (ca. 400AD), Augustine started the process by denying the idea of a mythical golden age, as originally stated by Hesiod (ca. 700BC), because it was contrary to Biblical Eden. The golden age was the basis of theories of rational law (such as Cicero's in 50BC), which use the goal of a new golden age to justify the righteousness of punishment. Then Augustine substituted a personal divine law of salvation in place of the golden goal. Augustine reasoned that no mortal, secular justice could ever be meaningful, by comparison to the far better achievement of all attaining eternal life. That first part much might have been OK by itself, but Augustine then went further to add a second part. He claimed that secular justice is not the virtue it appears to be, but rather results from the first deadly sin, pride, and thus is not safe, and moreover a danger to faith itself. He even went as far to call secular justice a 'weakness, plague, and disease/'.
The resemblance of at least the first half of Augustine's thought to Islamic doctrine might not be a coincidence. The consequences of the second half of this doctrine, in both religions, has been rather similar. In the West, this specific doctrine was a primary force leading to the Dark Ages, and the supremacy of divine law slowly eradicated all secular practices until the reformation. In the Middle East, there was an attempt by some, such as Averroes, to reconstruct secular law, but sectarianism caused the collapse of the Moor civilization and such notions were abandoned, leading to the current situation.
Did Mohammed directly coopt Augustinian Doctrine into Islam?
If one considers the topic without bias, it is not unreasonable to postulate that Mohammed actually picked up the first part of this doctrine from Augustine's doctrine directly, and acknowledging that would go a long way to resolving problems which the second part is still causing. So before discussing the real issue, the possibility of 'direct transmission' is first explored.
With all the Christians killed for public enjoyment in Roman games, one might be sympathetic with Augustine's condemnation of human law. Augustine was certainly well received at the time. He was incredibly popular, and his message indisputably powerful. His ideas spread like wildfire, as new and ever larger armies of evangelists took his message to all corners of the earth, unafraid of suffering or death, due the far greater joy of bringing others to eternal life. This of course included Syria, where St. Paul famously received his conversion.
At the time of Mohammed's birth, Syria had become a prosperous province of the Byzantine empire. Mohammed was taken to Syria as a child, so he first encountered the glowing promises of eternal life there somewhere around the age of 10 (~580AD). By that time Syria had perhaps a quarter million Christians in about a hundred different ecclesiastical systems, so it's really impossible to know what he specifically encountered there, except for one meeting with a heretical Christian hermit who named him the new living God. Details have been recast by generations of both Christians and Muslims in accordance with their own beliefs, so now there are half a dozen legends that describe the specific facts in rather incompatible manners. What we do know is that Mohammed was not a scholar himself, and was never taught Latin or Greek, or even how to read and write. So he would have learned whatever he did about Christianity from derivative sources in sermons and personal accounts by the Christians of the time.
When Mohammed was about 40 years old, he then wrote the 'pulpit rhetoric' equivalent of Augustine's more academically stated conclusions in "City of God," most prominently in a Surah sometimes labeled as 'the citadel,' or 'the fortress.' Most major cities were already walled by then, so the correlation with Augustine's 'City of God' is so obvious, it is rather puzzling why no one else points it out.
In the Middle East, derivative rhetoric persists to this day, and it is on these specific passages in the Qur'an about divine law of salvation superseding secular law that radical Islamic terrorism draws the most, using exactly the same Augustinian concepts which caused the Roman Empire to collapse.
The Christian Precedence for Justifying Terrorism
Whether such a notion was directly inspired by Augustinian thought or not, from the perspective of ideology, it was rather irrefutably Augustinian first. Augustine is a founding father of the Christian church, and this notion was part of his doctrine first, regardless how right or wrong it was then, or is now. It had the same consequences to Rome as it is having in Islam now. No one has ever challenged the power and influence of Augustine's "City of God" in causing the downfall of Rome. No one can challenge that Augustine's opinion of secular law is repeatedly cited in defense of radical Islamic terrorism. Thus I can stand behind the assertion that Radical Islamic Terrorism is caused by Christian doctrine with fair confidence.