Why did the American colonists go from being proud, loyal citizens of the greatest empire in the world to rebels who wanted independence from that same empire?
The basic reason why this happened is that the Americans were "outgrowing" their role as a colony just as Great Britain was trying to exert more control over them. This is analagous to a family in which a child has been given a great deal of freedom, only to have it taken away when he or she becomes a teenager. This is a recipe for rebellion.
Before the French and Indian War, the colonies were given a considerable amount of freedom. The British treated them with what has been called "benign neglect." They imposed relatively few laws on the Americans and did not enforce those laws very vigorously. They did not place many taxes on the Americans and they allowed them to have a great deal of self-government.
After the French and Indian War, all this changed. The British felt they needed more from the colonies since they had just spent so much money on the Seven Years' War. They started to impose taxes and they started to vigorously enforce laws. They were doing this just as the American colonies were coming to feel more as if they deserved independence. The colonies were growing in population and economic power and were feeling that they shold have more autonomy. At just this point, the British decreased this autonomy. This was the real cause of the rebellion that led to the Revolutionary War.