Complex sentence: In the 1850s, Pike switched his allegiance to the Know Nothing Party due to the Whig Party's reluctance to embrace slavery and sided with the Confederacy when Southern states seceded from the United States in 1861.
Split into simpler sentences: In the 1850s, Pike switched his allegiance to the Know Nothing Party. He sided with the Confederacy when Southern states seceded from the United States in 1861.