Answer:
The Union victory that opened central Georgia to invasion was Chattanooga.
Step-by-step explanation:
The battle of Chattanooga was fought during the Civil war in 1863 by the Union forces and the Confederate troops. There were battles at Missionary Ridges and Lookout Mountains but they were called the Chattanooga Battles.
During the war, the Confederate troops were defeated forcing them back to Georgia where they had to end the railroad blockade which paved way for more invasion. In 1864, Georgia was invaded by General William Sherman's troops as a part of the Atlantic Campaign. All the fights for the campaign were won and Sherman capture Atlanta.