Why did the colonists fight the American Revolution?

The colonists fought the American Revolution to secure independence from Great Britain. They had a long list of grievances—most notably, taxation without political representation—which had not been addressed by the mother country. Over time, it became obvious to the majority that an amicable solution to the political conflict between the British and the Americans could not be reached and that some kind of revolution was unavoidable.
The decision wasn't taken lightly; at that time, Great Britain had the strongest armed forces in the world. To most neutral observers, it seemed that the Americans didn't stand a chance. But the Americans felt that they had no choice; they'd been backed into a corner and had no alternative but to stand and fight, whatever the consequences. A tradition of liberty had grown on American soil and it was widely believed that that tradition was under serious threat from continued British rule. To many, such as the great Patrick Henry, the choice was clear: liberty or death. And so the Americans chose to fight, and in doing so, changed the course of history.