The question you pose seems to ask for a scientific clarity that is not possible to achieve - in highly complex situations like this, it's impossible to establish exactly what the driving forces behind social change were. When there are multiple motivations and social forces competing, the histories that are written after the fact usually say much more about our need to create explanations rather than to pin down true cause and effect. We can often agree that one or a more factors were highly likely to have had strong correlation with the results - not all resides eternally within shades of gray. But these are still theories, not fact, in a world where we may not even be able to explain ourselves why we made certain decisions among various competing incentives, threats, and motivations. Bottom line is this - usually correlation is the best we can establish, and anyone who declares authoritatively what explained the results of the Surge is either overconfident, ignorant, or looking to push an agenda. To say that one cause was the predominant one - for any position - in complex social situations says more about the biases of the author that it does about what drove the actual situation. It's also why the history of even long past events is constantly changing as new evidence emerges, and new historians bring their own experiences and biases to the data set, usually choosing the data that confirms their previously held beliefs.