Secession of the Southern States started the war. They seceded to preserve Slavery.
The rich needed to preserve Slavery because they had so much money tied up in Slaves.
Normally, I would write your statement off as the meandering of an ignorant and uneducated fool - but I'm going to call bullshit because I suspect you know your statement is shit, and made it for partisan reasons.
The agrarian South had a nearly feudal structure, with a landed gentry wielding enormous political and economic power, while the majority lived as virtual serfs. The fact that 90% of whites in the Antebellum South lived in abject poverty, makes the claim of slavery as a root cause utterly absurd. Only the larger land owners could afford slaves.
The greater fear of the serf class was the competition posed by slaves. Often it was free whites who suffered most from slavery, as the agricultural jobs were filled by slaves, leaving them to literally starve to death.
The Antebellum South was not a pretty place for most people, black and white.
Contrast this with the North that was well into the industrial revolution. Despite the bullshit the leftists spew, industry was the salvation of the masses. Suddenly, the question of survival no longer depended on a healthy crop, but instead just labor at a factory. These masses became consumers who increased the fortunes of the remaining agrarian community in the North. To make matters worse, animosity toward the South, by the North, led to the importation of goods for manufacture from Europe. Particularly cotton, which was imported from France. The North was waging a form of economic warfare on the South long before the shooting war.
The socioeconomic situation in the Antebellum South was not viable, if left alone, it was destined to collapse. This went way beyond slavery, into the structure of the states, who could not sustain the existing infrastructure.
The war was between a fading agrarian society structured into virtual feudalism, and an emerging industrial powerhouse.
Slavery was at best an ancillary issue.