Final answer:
The victory at the Second Battle of Bull Run led the South to engage in the Battle of Antietam, which, although not a decisive win for the Union, allowed President Lincoln to issue the Emancipation Proclamation.
Step-by-step explanation:
The big victory that led the South to the Battle of Antietam was the Second Battle of Bull Run, which occurred in August 1862. General Robert E. Lee's Confederate forces defeated Union troops, leading them to push into Union territory with confidence. This momentum brought them to Maryland, where the Battle of Antietam took place on September 17, 1862. Despite significant casualties on both sides and a tactical draw, President Abraham Lincoln viewed the Confederate withdrawal as a strategic Union win that enabled him to issue the Emancipation Proclamation.