shall be then, thenceforward, and forever free
On September 22, 1862, partly in response to the heavy losses inflicted at the Battle of Antietam, President Abraham Lincoln issued a preliminary Emancipation Proclamation, threatening to free all the slaves in the states in rebellion if those states did not return to the Union by January 1, 1863. The extent of the Proclamation's practical effect has been debated, as it was legally binding only in territory not under Union control. In the short term, it amounted to no more than a statement of policy for the federal army as it moved into Southern territory.
In larger terms, however, Lincoln's decision to issue the Emancipation Proclamation was enormous. This event, combined with the determination on the part of African Americans to flee across Union lines as the federal army advanced into Southern territory, framed the Civil War as a struggle for freedom and against slavery. In more practical terms, the issuance of the Emancipation Proclamation prevented European nations from intervening in the war on behalf of the Confederacy and enabled the Union to enlist nearly 180,000 black volunteer soldiers to fight between January 1, 1863 and the conclusion of the war.