In the early days of British colonization, the British gave the colonists a lot of self governing powers and autonomy, and it remained this way for several years. However, when King George III took power he tightened the grip on their colonies a lot more, which created some tensions. One big thing was after the French and Indian War, the British heavily taxed the colonists with things like the Stamp Act because it has cost the British government a lot of money to defend the colonies in the. This angered a lot of colonists because they were getting taxed without consent in that they have no representation in Parliament. Although other British colonies also did not have representation, the colonists felt that they were just as valid as British citizens as those in GB, so they were angry that they had to pay all these taxes without agreeing to them. Hence the phrase "no taxation without representation"
The British abandoned Boston in early 1776 because they were forced out of the country by the American soldiers.
American Revolutionary War was at large, and the Patriots, led by general Washington (who later became the first president of USA) won the battle at Boston, which was bloodless, by the way. This brought an end to an eight-year British occupation of the city.
England was the first to split.