Lincoln's first Inaugural Address, he stated that he had "No purpose, directly or indirectly, to interfere with the slavery in the States where it exists." That changed when the Civil War bursted out. The Civil War: April 12, 1861- May 9, 1865. In the beginning of the war, Lincoln thought of of the problem as a preservation of the Union rather than abolishing slavery. His opinion changed when thousands of slaves fled to join Northern armies in mid 1862.
In mid summer of 1862, Lincoln persuade his idea to the cabinet. He proposed his idea of "The Emancipation Proclamation". He told his cabinet that if these slaves were freed, the Confederacy could no longer use them as laborers.
On September 22, 1862 Lincoln issued "The Preliminary Emancipation" after the win at Battle of Antietam. The Preliminary Emancipation Proclamation went into affect on January 1, 1863.
January 1, 1863, The Emancipation Proclamation was into affect. The Emancipation Proclamation stated that, "All persons held as slaves within any State or any designated part of State, the people whereof shall then be in rebellion against the United Stated shall be then, thenceforward, and forever, free." Even though the Emancipation Proclamation did not have a right away change, it freed about 3,000,000 slaves.
The Emancipation Proclamation wasn't under legally the Constitution. In 1864-1865, the Republican Congressed passed the Thirteenth Amendment which took a huge stand in history.