The Battle of Glorieta Pass, in the state of New Mexico in which I currently reside in, was the farthest west the Civil War ever went. There might have been small skirmishes elsewhere that I'm unaware of, but the largest engagement of the Civil War in the western theatre was fought in New Mexico.

I have read a few books that only cover the east coast engagements--Gettysburg, Bull Run, Seven Days and Antietam--that only give a glancing look at the western theatre. As its been said many times before, the fall of Vicksburg effectively cut the Confederacy in half and was tantamount, in strategic terms, to R.E. Lee's defeat at Gettysburg.

In Shelby Foote's Civil War Narrative he writes in the author's note that his goal was to bring more attention to the western theatre and to the various naval engagements that were fought during the war. There are certainly many books that will do that--Foote's being one of them.

Here's a great link to an article that was recently published on the battles that were fought in New Mexico. It contains a link at the bottom to the author's expanded work on the New Mexico campaign between Canby and Sibley.

In my opinion, most casual students of history find it more interesting to learn about the exploits of U.S. Grant, R.E. Lee, George McClellan, and Stonewall Jackson in the eastern theatre. There's something about Lee invading Maryland or Pennsylvania that always gives the reading a more interesting tone for me. I figure part of the reason for this was the proximity that all of these battles were fought in relation to the capitals of the Union and Confederacy. When Lee invaded the northern states the question was would he make a run on the northern capital? New York City? Baltimore?

When McClellan and Grant were on the doorstep of Richmond would they be able to seize the Confederate capital and the Confederate government?

In essence, it's like the difference in chess between going after a pawn or a rook as opposed to a king or queen. The circumstances, at least to the casual eye, make it more exciting to learn about the capture or almost capture of the king or queen. If the Confederacy had been able to capture Washington D.C. in 1862-1863, hypothetically speaking, this would almost have assuredly led to European intervention on their behalf. I'd say the battles in New Mexico were the equivalent of capturing or battling for a pawn--it mattered but not as much as the other pieces. Whereas the Battle of Gettysburg and the fall of Vicksburg would be the same as damaging or capturing a queen or a knight. Maybe damaging is the wrong word to use for Gettysburg, but in chess you can get to a point where you take the queen out of play because of a position you've put it in. I think that effectively describes what happened to Lee's Army of Northern Virginia after Gettysburg for a short while at least before the Wilderness campaign. Whereas the Union capturing Vicksburg was the equivalent of taking that piece off the board altogether.

But the cool thing about all the campaigns or battles that were fought is they were all like going after a piece on the chessboard. While Glorieta or Red River might not have been as exciting as going after the king or the queen they were still fascinating nonetheless and influenced how the rest of the war played out. Just like in chess, it's very difficult to capture the king or the queen in the opening moves when playing against an adroit opponent. It's only after eliminating the smaller pieces on the board that you're able to go after the larger ones. It was only after the Union captured their opponents or held on to their pawns, rooks, bishops, and knights--New Mexico, Chattanooga, New Orleans--that they were finally able to bag the queen and king--Richmond, Atlanta, and the Army of N. Virginia.

So when people try to write and talk about the Civil War in a general fashion, I think they try to give the most interesting details up front and allow the listener/reader to go searching for the other parts of the chess board after they've got them involved in the game. This was certainly my approach when I started learning about the Civil War ten years ago and the tactic I employ when I try to teach people about it.