First of all it wasnt cemetery hill, it was culps hill that Ewell didnt take, it commanded the town, and Lee was the reason the south lasted so long. He was the greatest commander ever. Tactics today are based on him, speed and mobility. And slavery didnt become an issueuntill the emacipation proclamation, and it only applied to states still in rebellion and they were not gonna give them. Lol so in essence "the great emancipator" didnt free one slave the 13th amendement did.
I'd say you are correct on slavery not being an issue for the North before the Emancipation Proclamation, but it was certainly an issue for the South. Why do you think they seceded in the first place?