Why did the south have a lot of success in the east?

I think it’s because of the tactics and general. Robert E Lee was deployed in the East since Richmond was their Capital. Lee was a tactically aggressive commander and far more competent than the mediocre Southern generals in the West. Though he took an enormous number of casualties, he turned back McClellan's forces in the Seven Days battles. but then Richmond fall

The goal of at least one group in a limited war is to maintain its freedom and preserve itself.