The document that declared the independence of the thirteen American colonies from Britain is the Declaration of Independence. Adopted on July 4, 1776, by the Continental Congress, it was primarily drafted by Thomas Jefferson, along with contributions from Benjamin Franklin, John Adams, and others. The Declaration outlines the colonies' grievances against King George III and asserts the inherent rights of individuals to life, liberty, and the pursuit of happiness. This landmark document not only formalized the break from British rule but also laid the foundation for the United States' democratic principles.