How were the border states different from the others?
The border states in the Civil War in the United States had fewer slaves per capita than the rest of the south. Also geographical features made it easy for the North to invade them and difficult for the South to defend them. The wide Potomac cut off reinforcements to Delaware and most of Maryland. The mountains made Kentucky difficult to supply from the south. Missouri was surrounded on 3 sides by Union states. As a result, it did not make sense for those states to pull out of the Union. A number of solders from those states joined the Confederate Army, but the states did not side with the confederacy.
There are 2 US states that have no common border with any other state. These are Alaska and Hawaii. The remaining states are collectively considered the 48 "lower" or "contiguous" states. (Alaska would be considered the 49th continental state.) Hawaii is an island, and Alaska has a land border only with Canada, which is a different country.