There were many reasons for a Civil War to happen in America, and political issues and disagreements began soon after the American Revolution ended in 1782. Between the years 1800 and 1860, arguments between the North and South grew more intense. One of the main quarrels was about taxes paid on goods brought into this country from foreign countries.
Northern and mid-western states were becoming more and more powerful as the populations increased. Southern states lost political power because the population did not increase as rapidly. As one portion of the nation grew larger than another, people began to talk of the nation as sections. This was called sectionalism.
As the nation grew in size, so did the opportunities for expansion westward. Many felt that slavery should be allowed in the new territories such as Kansas and Missouri, while others were set against it.
The debate became very bitter. Southern politicians outwardly charged that their voices were not being heard in congress. Some Southern states wanted to secede, or break away from the United States of America and govern themselves. Emotions reached a fever pitch when Abraham Lincoln was elected President of the United States in 1860. He was a member of the Republican Party and vowed to keep the country united and the new western territories free from slavery. Many Southerners, who were Democrats, were afraid that Lincoln was not sympathetic to their way of life and would not treat them fairly. The growing strength of the Republican Party, viewed by many as the party friendly to abolitionists and northern businessmen, and the election of the party's candidate was the last straw. Southern governors and political leaders called for state referendums to consider articles of secession.
Slavery to most non-historians is the reason. But from the lincoln diaries, lincoln confessed, if the south would come back, he and congress would not allow slavery abolished. And would let western states decide for themselves. But since they didn't because of taxes and representation, lincoln decided to just ship them off to other countries when freed. Which was his plan since before starting public office. But the restoration of the south was so costly, they didn't relocate the slaves.
And we have what is called the bloodiest period in our history.