The defining moment in U.S. History that occurred in Philadelphia on July 4, 1776 was the adoption of the Declaration of Independence. This pivotal document formally declared the thirteen American colonies' separation from British rule, articulating their collective grievances and the principles of governance based on individual rights and self-determination. The Declaration, primarily authored by Thomas Jefferson, not only signified the birth of the United States but also served as a foundational text for future democratic movements both domestically and globally. Its celebration on Independence Day has become a cornerstone of American identity.