The document that declared the independence of the thirteen American colonies is the Declaration of Independence, adopted on July 4, 1776. Drafted primarily by Thomas Jefferson, it articulated the colonies' grievances against British rule and asserted their right to self-governance. This document signified a revolutionary break from colonial authority, emphasizing fundamental principles such as equality, unalienable rights, and the pursuit of happiness. Its adoption marked the establishment of the United States as a separate nation, inspiring future democratic movements worldwide and laying the groundwork for the Constitution that would follow.