The Declaration of Independence declared the thirteen American colonies free from Great Britain.
The document announced that the colonies were no longer politically connected to the British Crown and should be regarded as independent states. Its argument followed a list of grievances against King George III and a statement that governments derive their authority from the consent of the governed.
The conflict behind the Declaration was the American Revolutionary War, which had already begun in 1775. The Declaration transformed the military rebellion into an explicit claim of national independence. Britain continued fighting the war until the Treaty of Paris in 1783 recognized the United States as independent.
“Great Britain” is the standard answer in this context, though the political structure involved the Kingdom of Great Britain and its government. The Declaration itself refers to “the British Crown” and “the King of Great Britain,” not to France, Spain, or another European power.