Why did the Colonists win the Revolutionary War? America was not at the center of the world at the time. England was. Great Britain was slow to understand the nature of the threat of war with America and its colonies.
Americans were a bunch of rag-tag but hearty fighters dedicated to an idea. The idea was quite real. It was an idea of personal liberty, freedom and self-government.
The soldiers fighting for England were fighting for their empire or they were being paid to fight for it. When you are fighting for something more personal you are more devoted to the purpose of the fight. It is more personal. It means more to the fighters.
They just needed a good and talented, and dare I say, an inspired and inspiring leader. They got that in General George Washington. The men followed him, loved him, and for the most part, obeyed him. They ultimately knew they were fighting for what was right.