Are you looking for a specific word? The answer is border but I see you've included this in your question so I believe you do not understand the concept.
The answer is B) Madison acted correctly.
Answer:
During the crusade, Frederick I, Holy Roman Emperor, had almost besieged Constantinople because of the failure of the Byzantines to provide him with safe passage across the Dardanelles. The Byzantines for their part suspected him of conspiring with the breakaway Byzantine provinces of Serbia and Bulgaria.
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