There's some fantastic lectures made available by the US Army War College on youtube. Link to their youtube channel.
Really enjoyed this recent one, which goes through the context of the Gettysburg Campaign in terms of a strategy of exhaustion from the Confederacy and Lee's appreciation of what he needed to do.
[video=youtube;lrXxz4iniRs]https://www.youtube.com/watch?v=lrXxz4iniRs[/video]