Simplify the following text for a Grade 9 native English-speaking person.
Original: The United States Declaration of Independence is a statement adopted by the Continental Congress on July 4 , 1776 , which announced that the thirteen American colonies then at war with Great Britain were now independent states , and thus no longer a part of the British Empire .
Simplified: The United States Declaration of Independence is an important document in the history of the United States of America . It was written in 1776 and says that the American colonies were no longer under the rule of Great Britain , but were a new country .