[edited] According to Washington Post, "There is a consensus among historians that the root cause of the Civil War was slavery". Assuming that slavery was indeed the root cause, I can understand why the South would be willing to go to war to maintain it: because their economy depended on it to a very considerable degree. But why would the North care so deeply about this issue as to allow tensions to escalate into a war? I imagine abolition would indirectly hurt them economically as well, and it does not seem likely that their objections were purely moral in nature, if racist laws remained in force for a long time after the War. Or is it not the case that slavery was the root cause?
You are confusing two questions:
What was the root cause of the Civil War?
Why was the North going to the war?
- North was not going to the war over slavery.
a. Before the war, already northern-dominated (after southern states seceded) Congress passed the amendment protected slavery:
b. Already during the war, Lincoln issued preliminary emancipation proclamation, practically stating that if southern states would stop fighting and return to the Union by 1863, slavery would be intact:
North was going to the war to suppress an armed rebellion - Confederacy was already building army (up to 100 thousands strong, with US army at that time about 16 thousands), and attacked US army installations.
- However, slavery definitely was the root cause of the war - if not single, at least by far most important.
Seven southern states seceded from US, because they demanded from federal government unlimited extension and protection of slavery beyond the borders of slaveholding states, and recently elected president (Lincoln) belonged to the party with main goal to contain slavery were it is already exists. Everybody understood that containing slavery would lead to its ultimate extinction. So if not slavery, no secession and no war would occur.
- It is tempting to say that South was going to the war over slavery. The answer is not so simple.
Sure, South was willing to go to the war over slavery, but it was no need over slavery - because North did not attack slavery when South started the war.
In my opinion, Confederacy started the war, because peace perspective were very bleak.
Seven cotton states practically did not have industry, adequate merchant fleet, financial institutions, and even adequate food and mule production; they were dependent on other states on almost everything. They practically have only cotton to export, it is why Confederate constitution removed the ban on taxing exports. Two cotton-producing states (Arkansas and Tennessee), being in northern Union, would compete with Confederacy cotton production on favorable terms. Pre-war Confederacy have dangerously high proportion of slaves, and lost Fugitive slave laws protection.
Secessionist counted on most slaveholding states to join them; it did not happened peacefully. On April 4th 1861, Virginia secession convention voted against secession, and a three-man delegation was sent to consult with Lincoln, who prior inauguration publicly discussed with virginian Fort Sumter evacuation in exchange of Virginia stays in the Union.
The only way to bring Virginia and other slaveholding states to Confederacy was the immediate war, and the war came - April 12 confederates bombarded fort Sumter. In a few weeks Virginia, Tennessee, Arkansas and North Carolina were joining Confederacy, increasing her white population twice and industrial and military strength much more.
I'm going to have to provide a bad answer because the question is ill focused, lacks evidence of research, and OP persists in debating in the comments rather than revising the question to resolve the issues about which comments have requested clarification.
The question seems to be an attempt to identify the role of American chattel slavery as a cause of the civil war. It contains the assumption that the North was responsible for pushing the South to war.
There are very few things in history that have a simple cause and effect relationship. (or perhaps there are, but we don't study them because they are trivial.) Slavery was a cause of the war. Fundamental tensions originating before the Constitution was a second cause of the war. Cultural divergence was a cause of the war.
The North didn't start the war; the South did. The South started the war because they didn't believe that the country could encompass the visions of both the South and the North, and because they believed that a non-military strategy would result in unacceptable losses for the South. They believed that the North wanted to eradicate the Southern way of life. The symbol of this was slavery, but their concerns were broader - there were irreconcilable economic and cultural differences - the 3/5 clause in the constitution, the Jay treaty, etc. etc. etc. The North sought a future for the country that included both freedom from slavery and prosperity. The North had made that clear from the foundation of the Republic.
The Southern political position was idiotic. The South sought a future based on a fantasy recollection of medieval life. Their vision was utterly unconnected from reality, and their economic principles were less sophisticated than your average third grader. They wanted to get rich by selling commodities in an unchanging world. They rejected industry, credit, capitalism, and every vestige of modernism. They created a fantasy reality based on a bygone era where land was more important than capital. They held dances and wore fancy clothes and each generation was financially, intellectually and morally inferior to the last.
It is not possible to predict a person's view based solely on their economic class/interest By the middle of the 19th century there was a consensus that abolition and civil rights were the right choice even if that choice involved some economic hardship. Britain endured huge economic hardship to fight slavery on a global scale. The New York Abolition society had existed since the beginning of the Republic. For some people, civil rights were a religious imperative; for others an ethical or moral imperative that trumped their economic self-interest. The South rejected this consensus, slowly transforming from irrational to delusional to pathological zealotry. In the end they started what was the bloodiest war in human history to that point in order to silence the people who kept demonstrating that the Southern way of life was delusional, disconnected from reality, immoral, and economically stupid.
Was slavery a contributing factor to the civil war? Yes. But slavery was one element in a mix of tightly coupled factors that ultimately resulted in irreconcilable differences.
Unfortunately a full answer to the question would be more than book length - there have been multiple books on the causes of the civil war, more books on slavery, more books on the causes of war. Questions that require book length answers are out of scope for H:SE (See [help]). This is a bad answer because it includes no sources, no evidence of research, and has a few paragraphs of thought about a subject where an encyclopedia would be more appropriate.