Which event established atlanta as the busiest city in georgia?

The event which established atlanta as the busiest city in georgia was:

The Civil War in 1864 which burnt down most of the things in Atlanta.

Explanation: The Civil War was an issue which took major effect in Atlanta because most of the properties there were burnt. So after the Civil War the Federal state decided to make Atlanta the "Third Military District" which would oversee Georgia and some other states and also ensure rebuilding of major infrastructures.