What are the border states and why are they unique?

there are actually at least 3 different common meanings for the term border states

the first refers to the states of Delaware Maryland West Virgina Kentucky & Missouri during the American civil war

which were uniquely slave states that bordered free states & were aligned with the union

the second refers to the eastern European nation states of Finland Estonia Latvia Lithuania Poland Romania belarus & Ukraine

which uniquely won their independence after the Russian revolution & first world war

& the third refers at present to the states of Maine New Hampshire vermont New York Pennsylvania Ohio Michigan minnesota North Dakota Montana Idaho Washington Alaska California Arizona New Mexico & Texas

which are uniquely situated on the borders of the united states