At the beginning of the US Civil War, the "southern" border States were Kentucky and Missouri. In this answer, Maryland is excluded in that although it was a pro=southern slave State, it cannot be considered a border State.
Texas and Arkansas each border Louisiana. All three can be described as as "southern States".
The present day states were: Cananda, Florida, and the southern border.
Missouri's Southern border.
It banned slavery in any new states North of Missouri's Southern border.
The "Border States" were slave states.
Texas and Arkansas each border Louisiana. All three can be described as as "southern States".
Rio Grande forms the Southern border of the United states.
Arkansas
The present day states were: Cananda, Florida, and the southern border.
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The gulf that forms part of the southern border of the United States is the Gulf of Mexico
The Pacific, Atlantic and Arctic oceans border the United States. The Indian and Southern oceans do not border the United States.
Mississippi
Kentucky and Missouri
Boredom, retirement and luxury.
The states that make Florida's northern border are southeastern Alabama and southern/southeastern Georgia.