Slavery, by itself, cannot cause the Civil War.
There have to be two different economic systems. There was one system based on paid labor and another based on coerced labor.
The two systems have to be viable. If either system is clearly failing, the parties can just wait for economic collapse of the weaker system
The two systems have to be competing for resources, including land, capital and have some overlap as to markets.
The two systems were very much competing for land and capital and the physical separation of the two systems was declining and there was beginning to be some overlap, especially with respect to coal and iron production.
The differences between the paid labor economy and the coerced labor economy was the necessary pre-condition for the advent of the war, if the potential belligerents could not create a formula for the conversion to one system or the other.
But that was not enough to cause the war.
There had to be a sudden shift in demographic power. The shift had to be so rapid that previously dominant section could believe it was still dominant, in some way, if not in numbers.
That sudden shift occurred in 1850-1860 and the results of the 1860 showed that the decline in political power in South Carolina, Virginia and New York was continuing.
This sudden shift was sufficient to cause the belligerents to abandon politics and resort to armed violence.