Why was the Battle of Antietam important to the north?

Question

This is really impotant because I don't get it

Answer 1

 It gave the North ,momentum by a slight militarial victory but it gave Lincoln a chance to use its political fallout to issue the Emancipation Proclamation and change the direction of the war from preserving the Union to the preserving the Union and the abolition of slavery which was accomplished by an amendment to the Constitution after Lincoln's death.