Fear is defined in the dictionary as the following:
b (1) : an instance of this emotion (2) : a state marked by this emotion
Now why do I begin with this?
The definition you can read here is probably pretty close to your own idea of what fear exactly is. Something bad is going to happen, so you’re scared. That’s it. It is a limited, quite narrow take on the emotion, and incorrect for many reasons. Let me explain myself…
Fear is essential for survival. There is quite a lot of debate about whether animals have “higher” emotions, but one thing few people deny is that animals are able to feel fear. In animals, the dictionary definition is pretty correct. The anticipation of danger causes a mostly physical reaction of heightened awareness, cortisol and norepinephrine levels peak, the body goes into fight-or-flight modus. The “higher reasoning” gets shut down and the body responds on instinct to the proposed threat. As I said essential for survival. You can’t really start thinking out a battle strategy first when confronted with an angry predator.
In humans this process is more than just a fight-or-flight-reaction. It is the catalyzer for a whole range of emotions, going from love and affection to rage and anger. Fear is what essentially thrives us, and this thing we call society.
A beautiful example of this is the notion of how marriage registration statistics peak after disasters, natural or others. The confrontation with a life-threathening situation indeed induces an initial fight-or-flight reaction, but in humans it does something more. It has a special extra possibility: assemble. The stronger the fear when confronted with a threat, the more people will group together. Is it a coincidence that when a nation is threatened -by massive unemployment, an enormous immigrant flow, neighboring nations with a taste for war- its people will often elect a totalitarian regime? No. Fear does that.
Fear brings people together. Not love, not faith. The simple realization that one needs the others for survival is the strongest tie. Without fear, there is no relationship, no group, no society. Only when the other is needed, a truly strong bond can be formed.
Of all emotions, fear is also the most honest one. Because the “higher reasoning” (prefrontal cortex) gets shut down when afraid, scared people are unable to lie. A frightened person will tell you all you want to know. Fear is the strongest, and most powerful emotion. There are many emotions, and I can imagine a lot of people would object to this, but… fear rules them all.
We're All Mad Inhere 
Fear is also preeminent in our dreams. We can’t escape it. I’m not afraid of dying, but if you threatened me with torture, I’m yours. Animal fear, too–predator and predatee. The bigger beast is top dog. I guess fear makes the world go round.
True…
Fear is so fundamental in almost every process known to men, it is the most basic emotion a living creature is capable of experiencing.
Fear is what thrives us… All men, of all races and kinds, have a fear and will suffer under it or cope with it in a way that influences others. Without fear indeed this world might just not go round anymore…