What allowed Augustus to take control of the Roman world and create a new political structure?
I would argue that there were two major factors that allowed this to happen.
First, there was the fact that the Roman world had been in chaos for quite a while before Augustus came to power. People are always going to be more receptive to new ways if the old ways are seen to be failing.
Second, there was the fact that Augustus himself was very effective at making people like him. Augustus was able to end the civil wars and to make himself (if we can believe the historians of the time) very well-liked. When a leader is well-liked, he or she will be much more likely to be able to implement reforms.