Why did seceding states believe they had to leave the union

Because the newly-elected Lincoln refused to allow the creation of any new slave-states.

The President Elected, Abraham Lincoln, was a known anti-slavery activist and he didn't allow the creation of new slave-states. As consequences, since there were more states joining the Union, the most likely scenario was a congress dominated with states that would adopt politics that could be unfavorable for the Southern States.

c.

worked constantly and gave many sincere speeches about the importance of independence

answer; i believe the two groups were irish immigrants and chinese immigrants;