Most people think it was Kennsaw Mtn. Kennesaw Mnt battle was a small battle, and Sherman quickly gave up the idea of taking the mountain from dug in confederate forces. (I GOT THIS COMPLETELY WRONG). Kennesaw mtn battle was a major battle and victory for the confeds. Here are the stats that I researched today:
Battle of Kennesaw Mountain: June 27, 1864
Offense: union, defense: confed
Engaged:
Union:99,000
Confed: 50,000
Casualties:*
Union: 3,000
Confed: 1,000
Battle of Peachtree creek July 20, 1864
Union forces dug in on defense, confed forced on offense
Engaged:
Union:21,655
Confed: 20,250
Casualties: (national park service estimate.)
Union: 1,700
Confed: 6,506
Casualties defined as killed, wounded, captured/missing. When researching you have to be careful of mixing up the terms casualties and deaths. Deaths are always lower that casualties in CW battles. The Battle of Peachtree Creek was a defeat for the confederates and they continued to retreat and fight southward until finally ceasing their defense of Atlanta in meaning full way. Their railway supply lines were totally cut off by Gen. Sherman and Gen. Sherman had his railway lines intact because they were behind his 100,000 troops and well defended. The confederate railway lines were cut by sherman's forces.
Sorry for this misinformation that I posted.