Where did Antietam Happen?
The Battle of Antietam happened in four places. The cornfield, the church or little white house, Bloody Lane (during the battle, it was called Sunken Road, due to natural indents, used as trenches during the battle), and lastly, Antietam Creek, where the battle gets its name. This should give you the general (no pun intended) idea:
Why did Antietam Happen?
Confederate general Robert E. Lee had been winning many battles in the South, and he wanted to move the battle into the Union. Lee's army split up to strike Maryland in many places. Soon, they captured Sharpsburg. Their plan would have been secret, had one of his troops not dropped some cigars. Two Union soldiers found those cigars. Wrapped around them were the battle plans for Lee's army. They brought the plans to their general, McClellan. He could have attacked Lee when his army was whole, but instead attacked the division of 38,000 troops who had captured Sharpsburg. McClellan had an army of 75,000. They met at the cornfield, interrupting the Texans' breakfast! Normally a feisty bunch, the Texans blew their top. And so the battle began on September 17, 1862.
The Cornfield
The bloodbath began when Ricketts (Union) charged. Defending against him was Confederate general Lawton. One Union soldier stated, "We could see the glint of the Confederate bayonets even through the corn." Once in the field, no one could see where they were shooting. Bullets flew through the air, wounding both sides. No one could see a thing. Sides were shooting themselves as well. It was chaos. In the end, both sides fell back. At this early stage, the Union was losing, but its soldier reserve was far larger, and increasingly so with every fight.
The Church
The battle moved over to Dunker Church, also called by the generals, "The Little White House." The church had barely anything in it. Just a bible and some seats. Apparently there were muskets as well, because the anti-slavery priests fought along side the Union troops. Stonewall Jackson's (Confederate) troops met Sumner's (Union) in a hill near the church. The fight was deadly. After a little while, Anderson's (Confederate) troops reinforced Jackson's. McClellan refused reinforcement requests. Even so, the Confederates fell back.
Bloody Lane (Sunken Road)
General Sumner (Union) came against General Hill (Confederate) at Sunken Road. Sumner's men charged at the Confederates, who were stationed in the natural trenches that gave Sunken Road its name. One Confederate officer was shot six times, and survived to a ripe old age! The Union was repelled again and again, but in the end, it broke through Confederate lines. The Confederates fell back. Once again, even though the Union requested reinforcements, McClellan refused to give any.
Antietam Creek
The battle on Burnside Bridge, which was over Antietam Creek, was led by Union general Burnside and Confederate general Toombs. Though Burnside could have crossed the shallow creek, he decided to capture the bridge first. He attacked Toombs over and over again, but was repelled. He made one last attack saying, "Would the 51st New York and Pennsylvania regiments please lead this attack?" So before we continue, let's give a hand to New York and Pennsylvania! They were the last attack, but not because they lost. Burnside had more troops. The two regiments shattered the Confederate's last defense. Burnside was ready to attack Lee's camp, but McClellan told him to stand down. They could have ended the war, but they didn't. The bloodiest single day in the United and Confederate States had ended.
What Was the Effect on US History?
Antietam was the first major battle on US soil, and it was also the first major US win. Most people consider Gettysburg the turning point of the war, but I say it is the end of the turning point. Antietam was the beginning. Before Antietam, there was no major US win. Between Antietam and Gettysburg, there were both US and Confederate wins. And, as most people know, after Gettysburg, there was no major Confederate win. Also, most people consider the Gettysburg Address the most important announcement in US history, barring the Declaration of Independence. However, though important, all the Gettysburg Address was a speech. The Emancipation Proclamation (issued because of Antietam) freed every Confederate slave. After Antietam, Lee lost a quarter of his army! He lost 10,316 men. Though McClellan lost more troops (12,401) due to his excess caution, he declared victory. As well as issuing the Emancipation Proclamation, President Lincoln removed McClellan from command.