The statement that is true of the Emancipation Proclamation is:
It freed all slaves in states rebelling against the Union.
The Emancipation Proclamation, issued by President Abraham Lincoln on January 1, 1863, declared that all slaves in Confederate states (states that were in rebellion against the Union) were to be set free. It did not grant U.S. citizenship, the right to vote, or outlaw slavery entirely in the United States; slavery continued to exist in some border states and areas not in rebellion at that time. Full abolition of slavery in the United States was achieved with the Thirteenth Amendment, ratified in December 1865.