What in your opinion was the main cause(s) of the Civil War?

What in your opinion was the main cause(s) of the Civil War? In 1850, America was a prosperous and growing nation. However, by 1861 the United States was divided into two separate nations at war with each other. Beginning with the Mexican-American War, analyze the events from the 1840s to 1861 that led to the Civil War. Utilize and cite evidence from U.S. History, chapters 14 and 15.1.