Even though the battle of Gettysburg is more famous than the battle of Antietam it was the bloodiest battle of the war and changed the whole war. It changed the whole tactic of the war, from an offensive war for the south to a defensive war for the south. Both sides, the North and the South, also lost a lot of men. The Battle of Antietam played an important role in the Civil War because it caused the Confederate army to fight defensively for the rest of the war

The very first battles were very offensive battles. The battle of Fort Sumter was the first battle of the war and it was when the south invaded Fort Sumter. According to Wikipedia, “At 3:20 a.m., April 12, 1861, the Confederates informed Anderson that they would open fire in one hour. At 4:30 a.m., a single mortar round fired from Fort Johnson exploded over Fort Sumter” and at 2 pm, April 13 the Confederate army won. Another example of the South offensive strategy was the battle of Hancock.” According to Wikipedia “On January 1, 1862, Jackson marched north in bitter cold from Winchester to Bath with the objective of disrupting traffic on the B&O Railroad and C&O Canal. On January 5, after skirmishing with the retiring Federals, Jackson’s force reached the Potomac River opposite the garrisoned town of Hancock, Maryland. His artillery fired on the town from Orrick’s Hill but did little damage. Union garrison commander Brig. Gen. Frederick W. Lander refused Jackson’s demands for surrender”. He continued this while looking for a safe river to cross, but he couldn’t find it so he withdrew.

The battle of Antietam was the turning point of the south’s strategy. On the September 17, 1862, the Army of Potomac and the army of Northern Virginia fought all day long. According to the book Antietam, McClellan had a 3 step plan which would have General Hooker fight the Confederate on the left on September 17, 1862 then General Burnside would attack in the right flank on the Confederate and finally McClellan would attack the center of the battlefield. According to HistoryNet, one fourth of the union soldiers were from New York and twenty five percent of the South was from Virginia. The casualties according to NPS.gov and Army Center of Military History said “the causalities were around 23,000 people” and according to the Book Antietam both sides lost nine generals in the battle. In the end, the South lost so many men that they could not afford to invade any more.
After the battle of Antietam the Confederate army started fighting defensively for the rest of the war and eventually lost the war. An example of a defensive battle was the third battle of Petersburg. According to Wikipedia “It was a decisive Union assault on the Confederate trenches, ending the ten-month Siege of Petersburg and leading to the fall of Petersburg and Richmond, Virginia.” After this battle, a week later Lee surrendered. The final example is the battle of Haw’s shop, which according to Wikipedia was “After Grant's army escaped from the trap that Lee had set for it at the Battle of North Anna, it began to move again around the right flank of Lee's army, in a continuation of the maneuvering that had characterized the campaign throughout May 1864.” This battle lasted over seven hours and the Union won because the Confederate withdrew.
What if the South won the battle of Antietam? Would that have changed the outcome? Who knows, maybe it would have had the North in the defensive position. The battle of Antietam forced the south to fight defensively, causing the Civil War to be shorter. The South lost so many men they couldn’t not afford to invade the North again. It was a matter of time until the North invaded and won the war.