How did the secession of the southern states cause
a civil war?

well it says ”Secession summary: the secession of Southern States led to the establishment of the Confederacy and ultimately the Civil War. It was the most serious secession movement in the United States and was defeated when the Union armies defeated the Confederate armies in the Civil War, 1861-65.”

explanation:

allergens: overstimulate the nerve system

neurotics: attack nerve cells

mutagens: damage or otherwise alter dna sequence

generators: cause defects during growth and development  

carcinogens: cause unchecked cell growth

i hope you get the idea according to me these are the effects that happened.