I was just reading about the Overland Campaign and something came to mind. According to the coordinates on wikipedia, the two bloodiest engagements in the Seven Days (Gaines' Mill and Malvern Hill) took place about 12 miles apart. The Battle of the Wilderness and the Battle of Spotsylvania Court House occurred about 11 miles apart and within 1 day of each other. So why are Gaines' Mill and Malvern Hill grouped together into the Seven Days, but the Wilderness and Spotsylvania are each their own?