Best Stand-Alone WorkIn my opinion I don't think that there are any stand-alone works that adequately cover the history of the Civil War.
As 'cadets' were mentioned I'm guessing they may be more interested in the military aspects of the war. If so, in that respect, I would recommend two books that are excellent from that aspect. Both were written by Paddy Griffith.
Battle in the Civil War: Generalship and Tactics in America, 1861-65. A slim volume that covers all the main aspects of Civil War warfare. An excellent introduction to the strategy and tactics used in that war.
Battle Tactics of the Civil War. A more analytic and academic work. Covers it all really. [Flicking through it as I wrote this I noticed that in the Command and Control chapter Griffth even discusses the role of bugle calls.]
Best Multi-Volume WorkFor me it's still Foote's
The Civil War: A Narrative. It still remains my 'go-to' that I consult before wandering off elsewhere in search of more information.
You Didn't Ask, But ...I would also recommend any of Bradley Gottfried's 'Maps of ...' books (Link
https://www.goodreads.com/author/show/384511.Bradley_M_Gottfried). If he has written one about your favourite campaign or battle it's an invaluable resource. Each one is extensively researched but presented in simple manner where there is usually an average of one page of prose per map as you are gradually taken through the campaign/battles.
Wonderful books, I'm fortunate to have them all (one signed by the author). A few years ago Gottfried replied to my post on another forum saying that he did have the 1862 Shenandoah Valley Campaign on his to-do list (as well as the 1864 campaigns). Regrettably I'm still waiting for that one to be published.