Lincoln's decision to free the Southern slaves

On September 22, 1862, Lincoln issued a preliminary order that on January 1, 1863,¹ he would order the emancipation of all slaves in any state of the Confederate States of America that did not return to Union. None of the states in the Confederacy returned, so Lincoln signed and issued his executive order on that date, which, ironically, was only directed at states in which Lincoln’s government had no authority at the time. Those slaves in the territory Lincoln actually controlled, he left enslaved.² 

According to Northern Civil War author and contemporary, Daniel Wait Howe,

The grave question uppermost in men's minds was whether the Union could be saved at all; but, slowly evolving out of the doubts and perplexities of the situation, and beginning to assume definite shape, was another, destined to overshadow all other questions, whether it were best to try to save the Union with slavery or to try to save it without. The Radicals declared that it must be saved without slavery, but Lincoln hesitated and seemed to be groping his way.

In a letter to Horace Greeley August 22, 1862, President Lincoln revealed his logic in reaching his momentous decision: 

My paramount object is to save the Union, and not either to save or destroy slavery. If I could save the Union without freeing any slave, I would do it—if I could save it by freeing all the slaves, I would do it—and if I could do it by freeing some and leaving others alone, I would also do that. What I do about slavery and the colored race, I do because I believe it helps to save this Union; and what I forbear, I forbear because I do not believe it would help to save this Union.

On today's date, 1862, Lincoln made up his mind to cross his Rubicon. The war now would become a crusade to free slaves. However, a vast segment of Northern voters were not yet in agreement with Lincoln’s intention. The fall elections in 1862 went heavily against the administration, and there were large opposition majorities in states like New York, Pennsylvania, Ohio, and Indiana. Even in Illinois, the president's home state, there was an enormous majority against him. And in almost all the other northern states his Republican party lost their majorities.

¹ Indeed, Lincoln's will issue his executive order on January 1, 1863, recalled today as the Emancipation Proclamation.
² Actually, Lincoln emancipated the slaves in the nation's capital when he signed the District of Columbia Emancipation Act on April 16, 1862.

Source: Civil War Times, 1861-1865, Daniel Wait Howe