In addition to what has already been mentioned, it bears pointing out that the actual trigger for secession was based on extremely shallow reasons.
The trigger for South Carolina's secession was the landslide victory of Lincoln in the election of 1860 - where he got 40% of the vote in a four-way race and got 180 electoral college votes. By contrast the Southern pro-slavery candidate Breckinridge got 20% of the popular vote and 72 electoral college votes. Lincoln in fact basically got more than twice the support of the pro-slavery Southern candidate.
To make matters worse the landslide victory was almost entirely the Confederate's own fault. This was because they had refused to support Stephen Douglas - who ended up carrying 30% of the popular vote (50% more than Breckinridge). Douglas was in fact the favored candidate by most Democrats due to his moderate stance on slavery (showing again how it was the root cause of everything), but he had been essentially rejected by the Confederates for not being pro-slavery enough.
And to top off this macabre series of political blunders, South Carolina and the Confederates refused to admit that they had massively screwed up in the 1860 election. They instead rage-quit and seceded before Lincoln could even take office. For any sensible historian this demonstrates how it was impossible for Lincoln to have instigated the Civil War - he wasn't even running the country yet when the South seceded!
South Carolina's official letter of secession moreover was a monumental exercise in hypocrisy, as they cited the Declaration of Independence of 1776 as their guiding document. That's because the South Carolina politicians apparently missed these key words from the declaration:
Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes;
In short, the Declaration of Independence frowned upon rebellion for "light and transient causes". And Lincoln was certainly "transient" as he was an elected president with a fixed term and not a dictator. And the grievances of the South were exceedingly light and pointless given that he hadn't even taken office yet and hence could not make any move against the South!
This is why the South Carolina letter of secession cherry-picked and deliberately excluded this sentence; and such cherry-picking has remained the favored tactic of Confederate apologists for generations.
In reality, they simply butchered the Constitution and Declaration of Independence for their own political gain and whenever it was convenient. That's why they never actually quote these opening words of the Declaration - "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness." - because such a line would be entirely hypocritical for a state fighting in the name of slavery where men are not created equal.
All of this again does not change the fact that the slavery was the root cause of everything. But if we are to speak about other reasons for the start of the Civil War, it cannot be emphasized enough that the South's own catastrophic political blunders in the election of 1860 and the bungled and clumsy acts of secession themselves were the primary factors that triggered the war.