Complex sentence: Through the 1820s-1840s, however, Benton's and Calhoun's political interests diverged, with Calhoun increasingly using secession as a weapon to maintain and expand slavery throughout the United States.
Split into simpler sentences: Through the 1820s-1840s, however, Benton's and Calhoun's political interests diverged. Calhoun was increasingly interested in using the threat of secession as a weapon to maintain and expand slavery throughout the United States.