Effects of the battle of chickamauga?

Devastating Union defeat by Braxton Bragg, saved from total destruction by George Thomas.

William Rosecrans removed from command, replaced by US Grant.

Bragg pursued the Union army to Chattanooga, to which he laid siege, and it looked as though he would starve out the Union troops.

Grant managed to force a river-crossing that enabled a new supply-line, and he and Thomas drove the Confederates off the heights overlooking Chattanooga.