Lincoln withheld the Emancipation Proclamation he drafted in July 1862 until a favorable turn in military events. Encouraged by the repulse of the Confederate forces at the Battle of Antietam on September 17, 1862, on September 22 he presented his preliminary version of the proclamation to his Cabinet. Chase recorded the momentous occasion and quoted the president as declaring “my mind has been much occupied with this subject . . . I think the time has come now.” Lincoln issued the preliminary proclamation that same day.

(Transcription)

When the rebel army was at Frederick, I determined, as soon as it should be driven out of Maryland, to issue a Proclamation of Emancipation such as I thought most likely to be useful. I said nothing to any one; but I made the promise to myself, and (hesitating a little)—to my Maker. The rebel army is driven out, and I am going to fulfill that promise.