The French supported the Americans after their victories at Trenton and Soratoga. The Spanish and Dutch helped by keeping British rival forces busy in Europe. The British surrender at Yorktown came after a French blockade of the Virginia coast helped America ground troops defeat Britians army.
The British could and did win the battles and capture the cities, but the colonial army was always still there. A big advantage the colonists had was allies, eventually including France. Finally the French actually declared war on Great Britain and formally joined with the colonies in their fight. This led to the great victory at Yorktown.
