Complex sentence: On the other hand, western parts of Texas were a frontier during the Civil War and while largely settled by anglo-Southerners after the conflict, some parts are often more associated with the Southwest than the South.
Split into simpler sentences: On the other hand, western parts of Texas were a frontier during the Civil War. While settled chiefly by Anglo-Southerners after the conflict, some of these parts have still been more often associated with the Southwest than the South.