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the Mediterranean itself is a key seam between Europe and Africa/Middle East. In my mind, then, several states that line this historic sea are classic Seam States, such as Morocco, Spain, Greece and Turkey.
I see (I think). So Pakistan is a Seam State in that it hedges between Southwest Asia/Central Asia (like Afghanistan) and, geopolitically speaking, straddles the worlds of western democritization and the Middle Eastern world of Islam.
Maybe I'm wrong (can it be!). However, I wonder how useful the term is if it's that malleable. A distinction without a difference, in other words. Still, I salute you for searching out a meaning.