What is the area in the vicinity of the England and Scotland, and England and Wales. Land Borders called? (especially the North Wales area between Chester and Wrexham
Cryptic Clue: You steal one of these from the Army (and pluralise it)(7)

Marches?

Well spotted Jenny
I think looking at it from a different view.It could have been called Marshes? because they act as a natural barrier between townships (unbuildable land) But as the area was drained the old name stuck and became Marches?
Off the top of my Head isn't the Low lying area around Lincolnshire also called Marches? as well as being called the Fens?