What political arguments led to the discussion of secession around the time of the civil war?

Slavery

Explanation:

The moment leading up the civil war, the Federal government forced the southerners to end the practice of slavery and exchange it with machines/industries.

The southerners did not want to do it since their economy at that time was heavily reliant on slave labors.

So, the southern states decided to secede. They separated themselves from the Federal government's rule with the intention to form new  independent nations.

the enslaved people onboard suffered from illness with some frequency

the answer would be logic.