What was the battle that proved to be the turning point of the Civil War?

Answer 1

Gettysburg is the usual answer to that question. They call it Confederate High Watermark, and it signalled the end of Lee's ambitions to invade the North.

By chance, this Northern victory came on the same day as another highly significant victory in the West - Vicksburg, the last Confederate stronghold on the Mississippi.

The double event was announced to great rejoicing on the Fourth of July.

It could also be argued that the turning point was a few months earlier, at Antietam. This was the unexpected Northern win that gave Lincoln the credibility to issue the Emancipation Proclamation, which had the effect of keeping Britain from granting recognition to the Confederacy.

However, all these 'turning points' would have been in vain, if Lincoln had lost the 1864 Election - which he thought he would.

He was saved just in time by three successes - Phil Sheridan clearing the Shenandoah, Sherman devastating the Georgia farmland, and Farragut liberating the port of Mobile.