The Declaration of Independence as read by thenSenator John F. Kennedy. The Declaration of Independence was a statement adopted by the Continental Congress on July 4, 1776, which announced that the thirteen American colonies then at war with Great Britain regarded themselves as independent states, and no longer a part of the British Empire. Written primarily by Thomas Jefferson, the Declaration was a formal explanation of why Congress had voted on July 2 to declare independence from Great Britain, more than a year after the outbreak of the American Revolutionary War. The birthday of the United States of America—Independence Day—is celebrated on July 4, the day the wording of the Declaration was approved by Congress.