Was the main cause of the civil war and WHY

Slavery. Southern states needed the institution to help with their main source of economy; agriculture. Northern states, however, were primarily manufacturing states and did not have as great of a need for slavery.

Explanation:

Slavery. Southern states needed the institution to help with their main source of economy; agriculture. Northern states, however, were primarily manufacturing states and did not have as great of a need for slavery.

Explanation:

answer; /// i believe that the correct answer is (d)the huang he river valley;