 All but one infantry regiment and all of the cavalry and artillery units served most of the war in what was known as the "Western Theater", where there were few battles that were on the scale of those in the "Eastern Theater".Beginning in 1862, the Confederate States west of the Mississippi River were assigned to the Department of the Trans-Mississippi.All of the new unit raised and organized after May 1862 would remain in the Trans-Mississippi for the remainder of the war.