The answer to this question can be very different depending on what you mean by “causes” of the Civil War. If we are talking about root causes of the war, there are only really one or two. If we are talking about events that helped bring the war about, there are many.
For root causes, there were the differences between the Northern and Southern economies and societies. The Northern economy was diversified. It had manufacturing and farming. Its agriculture included the production of many different kinds of crops. Its workers were free. The Southern economy was not diversified. It was essentially all based on cotton. Its workers were largely enslaved. This meant that the North and South had very different agendas and interests and these differences led to the war.
The war also came about because of the societal differences. The North was an egalitarian society that was somewhat similar in outlook to our own today. The South was hierarchical and was dominated by planters who felt that they were an aristocracy. This, too, made the two sides feel very different from one another and helped the war to happen.
These differences meant that the North and South were always in conflict. This conflict played out over a variety of issues. One of the most important was the Fugitive Slave Act of 1850. This law made Northerners feel that the South was dominating the government and using the government to implement its own inherently unfair and barbaric agenda. This reaction angered the South and pushed the war closer. Another was the Kansas-Nebraska Act and “Bleeding Kansas.” Here, actual fighting broke out between those who wanted to make Kansas a slave territory and those who wanted it to be free.
All of these can be seen as causes of the war.