The document that declared the independence of the thirteen American colonies from Britain is the Declaration of Independence, adopted on July 4, 1776. Drafted primarily by Thomas Jefferson, the Declaration outlined the philosophical justification for independence, emphasizing the colonies' right to self-governance and the principles of individual liberty and equality. It articulated grievances against King George III, highlighting injustices and oppressive actions that justified the colonies' decision to break away from British rule. This pivotal document not only marked the birth of the United States but also inspired democratic movements worldwide.