The Proclamation provided the legal framework for the emancipation of nearly all four million slaves as the Union armies advanced, and committed the Union to end slavery, which was a controversial decision even in the North. Hearing of the Proclamation, more slaves quickly escaped to Union lines as the Army units moved South. As the Union armies advanced through the Confederacy, thousands of slaves were freed each day until nearly all (approximately 3.9 million, according to the 1860 Census) were freed by July 1865.