Gettysburg was devastating for Lee's army. Putting aside the fact that he lost 28,000 killed, wounded, or captured during the three day battle, he also faced a ten day retreat that consisted of almost constant fighting. There were nearly two dozen engagements. He lost another 5,000 men during the retreat. The men were irreplaceable. Lee had no replacements available. He didn't have the luxury of a seemingly endless supply of recruits like northern armies had. Lee also lost a lot of his senior officers at Gettysburg and during the retreat. Division commanders, brigade commanders, and so forth were lost, and they could not be replaced.