Fort Sumter was a minor skirmish in which no men were even killed. The Confederacy simply gained control of Fort Sumter.
The First Battle of Bull Run
July 21, 1861
This was the first major land conflict of the war. The Union tried to outflank the Confederates, who were fortified on a hill. The Confederates fell back to another hill and launched a successful counterattack, winning the battle. This loss crushed the Union's sky-high morale.
Battle of the Ironclads
March 8, 1862 - March 9, 1862
This clash between two new ironclad ships eventually ended in a draw. It also signaled the end of wooden ships in war.
April 4, 1862 - July 1, 1862
The Union army tried to push through the peninsula in Virginia to end the war. The Confederates pushed the fighting force all the way back to the edge of the peninsula, causing devastating losses for the Union.
Battle of Shiloh
April 6, 1862 - April 7, 1862
General Grant marched troops West and was going to attack some Confederate camps. Before reinforcements could arrive, the Confederates launched a sneak attack on the Union. The Union fell back, little by little, trying to buy time. It worked; the reinforcements arrived; they counter-attacked and gained all of the land back. It was a Union victory and began a train of victories in the West.
Battle of Antietam
September 17, 1862
Going into the battle, Lee had a plan to divide his army into four sections. The union got a hold of this plan and devised an appropriate counterattack. Through poor leadership though, the Union failed to properly press Lee's lines, leading to an incredibly bloody "victory" for the Union. This also resulted in the firing of McClellan and the issuing of the Emancipation Proclamation.
Battle of Chancellorsville
April 30, 1863 - May 6, 1863
The Union camped in a forest in a defensive position. The Confederate forces were able to outflank the Unions in the forest and decimate them. Causing what is called the greatest Confederate victory; however, they lost Stonewall Jackson to friendly fire in the same battle.
Siege of Vicksburg
May 18, 1863 - July 4, 1863
The Union led by General Grant sieged the fortifications on the Mississippi near Vicksburg after two unsuccessful assaults. The result was Union dominance of the Mississippi and many Confederate soldiers captured.