In 1776, Britain had 13 American colonies. Actually, Britain had more than 13 colonies.
It had 14 mainland colonies: the rebellious 13 plus Canada. It also had several Caribbean colonies. About 2 million colonists lived along the Atlantic coast. If you had traveled through these colonies early in the 1770s, you would have had a hard time finding people who called themselves American. Most colonists thought of themselves as Virginians or Pennsylvanians or New Yorkers. That began to change as the colonists got more and more angry at Britain. As they united to fight against their ruler, the colonists put aside their differences. They started to think of themselves as Americans.