A compromise concerning slavery was necessary to keep southern states in union true or false

its true. The Southern states even thought of leaving thus union

True? (maybe not, read below)

Explanation:

Depending on time if this is before the civil war the missouri compromise was formed balancing the slave and non slave state representation and thus power in congress

The civil war was started due to South Carolina seceding from the union because of the Tarrif of Abominations aka the nullification crisis era