The first battle of the Trans-Mississippi theater was the <a rel="mw:WikiLink" href="https://en.wikipedia.org/Battle_of_Wilson's_Creek" title="Battle ... by @wikipedia | Factiii
The first battle of the Trans-Mississippi theater was the Battle of Wilson's Creek (August 1861). The Confederates were driven from Missouri early in the war as a result of the Battle of Pea Ridge.
