Identify and discuss 3 major causes of the Civil War.

The central issue and cause of the Civil War was slavery, but there are at least three other factors relating to slavery that helped lead to war, mainly involving arguments over the political and economic control of slavery. Many Americans cite that arguments over states' rights caused slavery, and they would be correct in a sense.
However, the question becomes the states' rights to do what? Own slaves. While Lincoln did not run on a platform of abolishing slavery, Southerners nevertheless feared that his election in 1860 posed a threat to the institution of slavery. While Lincoln opposed slavery, he assured Southerners in his inaugural address that he would not act on slavery where it already existed. His opposition was to the spread of slavery, especially in the newly acquired territories of the West after the Mexican–American War.
This territorial expansion greatly increased tensions in the years leading to the Civil War. Each time the US acquired a new territory or each time a territory applied for statehood, fierce debates broke out about whether or not slavery would be allowed to spread to these areas. Congress attempted to settle this dispute with the Compromise of 1850, which dealt with newly acquired territories from the Mexican–American War. California was admitted as a free state, while the New Mexico and Utah territories would be granted popular sovereignty, meaning the residents of those territories would choose whether slavery would be allowed by law. The slave trade (but not slavery itself) was also abolished in Washington DC and, perhaps most important, the Fugitive Slave Act was strengthened to require Northern states and individuals to return escaped slaves to their owners and to require any suspected runaway to prove he or she was a free black. Thus many free blacks living in the North were kidnapped into slavery if they did not have proper documentation of their freedom, and many Northerners grew increasingly hostile to the "slave power" of the South that now seemed to be forcing them to take part in perpetuating a system they did not support.
Tensions over slavery emerged again with the Kansas–Nebraska Act in 1854, which created the territories of Kansas and Nebraska and opened them to popular sovereignty, therefore overturning the Missouri Compromise of 1820 that had banned slavery above the 36–30 line. Tensions turned violent in what became known as "Bleeding Kansas," as both pro- and anti-slavery Americans poured into Kansas in an attempt to vote on the issue of slavery in those territories. The Dred Scott decision in 1857 further angered abolitionists and anti-slavery groups when the Supreme Court ruled that African Americans could never be citizens and therefore could not have the rights of citizens.
By this point the newly formed Republican Party gained national prominence and ran on a platform of opposing the spread of slavery. Although Lincoln stated he would not abolish slavery in the South, in part because he did not think the president could constitutionally do so, his election in 1860 sparked the immediate secession of seven Southern states from the Union: South Carolina, Georgia, Texas, Tennessee, Alabama, Louisiana and Mississippi. In their Declarations of Secession, each state cited slavery and the perceived threat to slavery as a reason for their secession. States' rights were mentioned as well; each state wanted to preserve its right to maintain the institution of slavery and felt that any attempt by the federal government to limit or suppress that right was unconstitutional. Ironically, these states also stated that the refusal of Northern states to comply with the Fugitive Slave Law and the refusal of the federal government to force their compliance was a cause for secession.
Ultimately the war officially began after Confederate troops surrounded and took Fort Sumter in South Carolina in 1861. Over the course of the war, thousands of slaves would flee the South and fight on the side of the Union Army against their former masters.
http://www.digitalhistory.uh.edu/era.cfm?eraID=5&smtid=2