Complex sentence: Prior to the outbreak of the American Civil War, White was in support of preserving the United States, but his loyalties shifted following the Battle of Fort Sumter and other Union encroachments into the Confederate States of America.
Split into simpler sentences: Prior to the outbreak of the American Civil War, White was in support of preserving the United States. White's national loyalties shifted following the Battle of Fort Sumter and other Union encroachments into the Confederate States of America.