The turning point in the Civil War was the Battle of Gettysburg. It's considered so, because this battle stopped the one and only attempted attack in Union territory. It also had boosted the moral of Northerners, making them think they could possibly win the war, which they obviously did. Gettysburg was not the one and only Northern Incursion. The Maryland Campaign that led to Antietam preceded it. Gettysburg was the last Northern Invasion. [Also, the real turning point was Vicksburg: the closing of the Mississippi to Southern traffic.]
The Civil War campaigns were the complex of military operations aiming to reach a strategic objective like: seizing a strategic point or city, destroying or capture an enemy's army. The most important of them were: the Peninsular Campaign; the Vicksburg Campaign; Lee's Maryland Campaign; Lee's Pennsylvania Campaign; the Chattanooga Campaign; the Overland Campaign; the Petersburg Campaign; the Atlanta Campaign; the March to the Sea Campaign; Hood's Tennessee Campaign; the Appomattox Campaign.
Do you mean which campaign was the turning-point of the American Civil War? It was the failure of Lee's invasion of Pennsylvania, ending at Gettysburg - on the same day that Grant took the surrender of Vicksburg on the Mississippi. After that, the North was bound to win - subject to Lincoln winning the Presidential Election of November 1864.
El Alamein
The turning point was not a battle but a siege, the Siege of Vicksburg.
The Battle of Midway .
A turning point in the North African campaign.
Most historians and scholars believe the turning point of the American Civil War was the Battle of Gettysburg fought in July 1863.
The actual turning point was the fall of Vicksburg at around the same time.
Some historians considered it the turning point, previously, but, majority opinion now considers Vicksburg to be the actual turning point.
Vicksburg
The Battle of Gettysburg.