The Declaration of Independence announced that the thirteen colonies were leaving Great Britain.
In 1776, the colonies were part of the British Empire and formally subject to the authority of King George III. The Declaration stated that the colonies were no longer politically connected to Great Britain and should be regarded as free and independent states.
The document followed years of disputes over taxation, representation, trade regulation, military presence, and imperial authority. Its list of grievances was intended to explain why the colonies believed separation had become necessary.
Great Britain is sometimes called England in casual discussion, but those names are not interchangeable in this context. England was one constituent country of the Kingdom of Great Britain, which had been created in 1707 by the union of England and Scotland. The American colonies declared independence from the British state, not from England alone.