Was slavery the main cause of the civil war? explain why you agree or disagree

I think the cotton invention was the main cause of the civil war. From the cotton invention they had used people of color as sales began to boost up more people rebelled against this. (my own opinion)

In other words,

I agree that slavery was the main cause of the civil war because farmers had used slaves as a cheap and efficient way to do cotton work without losing that much money. Slaves were usually sold for around 800 dollars which made things way much better for  farmers. If farmers were to hire men, they would have to pay them monthly which would have a heavier cost. Think about it like this: Buy a phone for 300 dollars, or rent a phone for 30 dollars a month. In the end, buying a phone (one time payment) would be cheaper. Farmers didn't want to resort to hiring men as this would cost much. Therefore, a civil war had broken out.

what words? are you talking about to complet what sentence