The United States Declaration of Independence is the pronouncement

adopted by the Second Continental Congress meeting at the Pennsylvania State House (now known as Independence Hall) in Philadelphia, Pennsylvania, on July 4, 1776. The Declaration explained why the Thirteen Colonies at war with the Kingdom of Great Britain regarded themselves as thirteen independent sovereign states, no longer under British rule. With the Declaration, these new states took a collective first step toward forming the United States of America.

Source: Wikipedia