One hundred and fifty years ago on New Years Day, Abraham Lincoln signed the Emancipation Proclamation. Lincoln never liked slavery, and he recognized that having slaves gave the southern states advantages in the Civil War. For example, southern slaves worked as cooks or nurses on the sidelines to save soldiers energy for fighting.

In the summer of 1862, Lincoln decided to write an emancipation proclamation. The document declared that any slave in a state that was fighting Union soldiers would be free on January 1, 1863.

Before issuing his proclamation, Lincoln asked his cabinet members to listen to a rough draft. He told them he would use his powers as president in wartime to free slaves who might otherwise help the Union cause. His Secretary of State, William Seward, supported the idea of freeing slaves, but warned Lincoln that the Union army’s losses during the year might influence the public’s opinion. He suggested that the president wait for a battle victory before announcing the emancipation proclamation. Lincoln agreed.

When the South’s General Lee retreated from the North after the battle at Antietam, Lincoln publicly announced his intention to sign the proclamation on January 1, 1863. Some people doubted that he would follow through on his promise, but they were wrong. On the morning of January 1, Lincoln made a major change in the proclamation. Though it still said that “all persons held as slaves” within the rebel southern states “are, and henceforth shall be free,” he added that African Americans could join the Union army. Lincoln knew the Union needed the manpower. In fact, though they served in all black units, between 180,000 and 200,000 black men fought for the Union during the war.

Before he could sign the document, Lincoln and his wife Mary hosted a New Years Day reception at the White House. First government officials mingled with the president, and then the public was invited to stand in a line to shake the president’s hand. Afterwards, Lincoln went back to his office to sign the emancipation proclamation. Lincoln said, “I never, in my life, felt more certain that I was doing right, than I do in signing this paper.” His hands were so stiff after three hours of shaking hands that he waited before signing his name. He said, “If my hand trembles when I sign the Proclamation, all who examine the document hereafter will say, ‘He hesitated.’” After a few moments, Lincoln’s hand felt less numb and he put his signature on the historic document.

The Emancipation Proclamation didn’t free any slaves right away. It only declared the slaves in the rebel states free—something Lincoln could not enforce in 1863. The document was important because it changed the way people thought about the war. Now soldiers in the Union army were fighting not only to bring the southern states back to the Union, but also to free the slaves.