What southern state could not leave during the civil war?

Delaware. Delaware is a tiny state - it has only three counties. It was a slave state, like Maryland. Delaware borders only Maryland, and Maryland is in between Delaware and the rest of the southern states. Maryland tried to secede, and Lincoln imprisoned its governor and most of its state legislators without trial, and installed a new government in Maryland made up of pro-Union men. Delaware, seeing what happened to Maryland, did not even try to get out of the Union.