George III was King of Great Britain from 1760 to 1820. He was England's longest ruler before Queen Victoria, he is most well known for being the English King during the American Revolutionary War.
Answer: The Declaration of Independence.
The Declaration of Independence (July 4, 1776) announced that the Thirteen Colonies would regard themselves as independent sovereign states, and were no longer under the British rule. The Declaration contended that King George III had violated the agreement between himself as a governor and the Americans as the governed. This targeted King George III as the primary reason for colonial discontent.
King George III never fully recovered from the loss of the American colonies.