Complex sentence: Once the Civil War began, however, the majority anti-secession population of the Dayton area turned him out, and Vallandigham lost his bid for a third term in 1862 by a relatively large vote; but this result may not be strictly comparable, owing to redistricting.
Split into simpler sentences: Once the Civil War began, however, the majority anti-secession population of the Dayton area turned him out, and Vallandigham lost his bid for a third term in 1862 by a relatively large vote. However, this result may not be strictly comparable, owing to redistricting.