As a fit and necessary military measure for effecting this object, [preservation of the Union] I, as Commander-in-Chief of the Army and Navy of the United States, do order and declare that on the first day of January in the year of our Lord 1863 all persons held as slaves within any state or states, wherein the constitutional authority of the United States shall not then be practically recognized, submitted to, and maintained shall then, thenceforward and forever, be free.