By the end of the second year of the Civil War, President Lincoln determined that he needed to change his strategy in order to win the war. The prime element that motivated the secession of the South was the issue of slavery. By changing the focus of the war to a war designed to end slavery, instead of just a war to keep the union together, Lincoln felt he might be able to garner more popular support for the war. He delivered the Emancipation Proclamation at the start of the third year of the Civil War to change the focus of the war.

His Emancipation Proclamation did not free any slaves in the South, but it did begin the first steps to slaves attaining that freedom. It proclaimed that all men were entitled to their freedom and that when the Union army liberated the states from the rule of the Confederacy, slaves in those states would be free.
The proclamation was intended to act as much as propaganda as to act as a war device. It was also partially intended to place the entire world on notification that the United States would not support slavery and that the Union sided with the oppressed. This served the purpose of keeping other countries from entering the war on the side of the Confederates.
The proclamation also opened the door for the admission of blacks into the armed services. They were allowed to fight against the oppression that they had suffered under for so long. By the end of the war, over 200,000 men had served in the Union Army or Navy.
Finally, although the promises could not be acted upon at that stage of the war, they were made a promise to free the slaves when their home states were defeated. There was no action that could be taken at that time but as the war continued and states and lands came under Union control, Lincoln kept his promise and the words came true as the slaves were set free.
Lincoln could not enforce his promises at the time and wouldn't be able to unless the North experienced military success on the battlefield. At the time, this meant the Emancipation Proclamation didn’t affect the status of slaves. Blacks that resided in the North already were free men before the Proclamation, as those states had outlawed slavery previously, and slaves in the South couldn't be freed until the North won the war. Still, the proclamation did pave the way to eradicate slavery from our country.
Lincoln fully realized that the Proclamation was only a first step towards the ultimate goal of getting rid of slavery.
To take any further steps, the Union army had to attain victory. Following the victory, Lincoln encouraged the abolition of slavery to be included on the platform of the Republican Party. Thus, while Lincoln’s Proclamation had no real teeth to it and did not immediately accomplish the outlawing of slavery in all states, he made a Constitutional amendment against slavery a major point of his reelection campaign in 1964.
Lincoln realized that at the end of the war, there would be some states left where slavery was allowed and the only way around this fact was to get an amendment passed through Congress.
The purpose of the Civil War was to bring back into the Union those states that had decided to withdraw as a result of disagreement about slavery.
As defined by the Constitution and the Declaration of Independence, all states had entered into a contract with each other that could not be violated. That contract mandated that the signers and their states agreed to remain as a Union.
The secession of the Southern states violated this contract and therefore the Federal government stepped in to ensure an unbroken Union. The Civil War was focused on keeping the states together - not on eliminating slavery, at least at first.
Following Lincoln's election to a second term as President, Congress passed the thirteenth amendment to the Constitution that abolished slavery in all the states controlled by the Union. Lincoln kept his promise. The Emancipation Proclamation set the stage for equality and freedom.