Why were the border states important to the north during the civil war?

The border states were important during civil war because of their geographical positions and most importantly in loyalty of their strong ties to North as well as South.

Delaware, Maryland, Kentucky, and Missouri were regarded as the border states and also they were slave States that did not leave the Union so they kept so called questionable loyalty which was crucial to Lincoln administration.

They were slave states that could have joined the Confederacy