Why did the british have to stay within 15 miles of the coast during the revolutionary war?

The British Army during the American Revolutionary War served for eight years in campaigns fought around the globe. Defeat at the Siege of Yorktown to a combined Franco-US force ultimately led to the loss of the Thirteen Colonies in eastern North America, and the concluding Treaty of Paris deprived Britain of many of the gains achieved in the Seven Years' War. However several victories elsewhere meant that much of the British Empire remained intact