This is because both sides sustained approx. similar number of causalities.
Out of 75,000 Union Army soldiers, over 2,100 were killed and a further 10,300 were injured.
The Confederates had an Army of 52,000 out of which 2,770 were killed and 11,000 were wounded.
It is also called the Battle of Sharpsburg and is known as the 'bloodiest' day in American history due to the sheet number of men who lost their lives.
The battle was tactically inclusive, however, it was a strategic and political win for the Union
