The first site to report on this was Touch Arcade, which reported that "Game Labs's" Ultimate General: Gettysburg was removed for having Confederate imagery:
They then quoted Game Labs as saying:
We accept Apple's decision and understand that this is a sensitive issue for the American Nation. We wanted our game to be the most accurate, historical, playable reference of the Battle of Gettysburg. All historical commanders, unit composition and weaponry, key geographical locations to the smallest streams or farms are recreated in our game's battlefield.
...Therefore we are not going to amend the game's content and Ultimate General: Gettysburg will no longer be available on AppStore. We really hope that Apple’s decision will achieve the desired results. We can’t change history, but we can change the future.