Out of three causes, the first principal cause of the American Civil War was the Compromise of 1850. It was five laws passed to resolve issues about slavery in the crisis of 1850. The issues, mentioned by Henry Clay, were the "Five Bleeding Wounds." In the compromise, the California admission issue was resolved and it was admitted as a free state, also, there would be no more slave trade in Washington D.C., and the border dispute between Texas and New Mexico ended in favor of New Mexico. However, there is one issue that kind of generated the Civil War even though it was already compromised. It was the way the U.S. handle the Mexican cession was resolved with the "popular sovereignty", the concept that let the settlers of a territory to decide whether they accept slavery or not. This settlement somehow aggravated the problem between the North and the South in congress about the balance of free and slave states, then later on lead to South secession from the Union. The Fugitive Slave Act also involved in the problems because as it was stated, escaped black slaves had to be returned to their owners in the South. However, the North didn't want to intervene, even the Abolitionists there helped the ex-slaves to escape from the slave catchers. These issues between the North and South worsen the relationship between them and lead to the Civil War.
The second principal cause was John Brown's Raid at Harpers Ferry, Virginia. John Brown was an abolitionist who became famous after his standing at the Bleeding Kansas in 1885. His assault started in summer of 1859, and unluckily, he could only recruited less than 25 men and even five of them were African Americans. Furthermore, in October 1859, Brown's men succeed in seizing the arsenal then they waited for the word of liberty spread among the slaves as he intended to distribute the weapons. However, instead of spreading among the slaves, it spread among the whites and this made Brown and his men were attack.