Because they don't want that federal states would interfere between two states
Explanation:
There was a difference in opinion between Northern and southern parts of America regarding Federal and State governments.
Northern part supported the Federal government, but the southern part wanted state governments should be given more powers and they felt central governments would curb down their powers on slavery.
The civil war was contest between the northern and southern parts of the USA in order to abolish black people slavery in the year 1861-1865. Lincoln was the president of the USA during civil war.
