Fear is actually not a real thing, it's an illusion. But it is an illusion that is real enough for them, and clearly, for mankind also. The Chitauri saw that man, in the early stages of being, began to fear when they lost much of their psychic ability, and this is something the Draconians fed on. Thus, terrorism was introduced into the world. Claims that terrorists from Iraq and similar excuses were all made up by the Government to induce fear. The true terrorists were in fact those people that everyone turned to when it happened. These huge terrorist events fed the demons and do each time. They are not chance... they are planned long before they take place. By the very Government you trust.
As I mentioned before, Satanic rituals have taken place all over the world by some of the most notable leaders of the times. And this is important in the theory of fear feeding the demons. It has been stated by people present at such rituals that the demons will terrify the victim as much as they can before the sacrifice takes place. The reason for this is that the human blood, when afraid, contains the sustenance they need. They perform the actual sacrifice when the victim is most afraid, then pour the blood into a goblet to drink it from. This has been seen by eye witnesses who were dragged along to such rituals and were lucky enough to not die there.
This is how they work. As long as mankind is afraid, the Draconian demons win. This is what I have discovered.