A reason for the longevity of the Byzantine Empire is how they managed their foreign relations. When excluding the Roman Empire of which the Byzantine Empire is a direct continuation of, it still stands as the longest living regime to have ruled in Europe (and second in the world only to Japan). Armed combat was the primary method with the evolved traditions of the Roman Empire, however Byzantine diplomacy which eventuated with their many treaties was used extensively as well. A lot of what we know of the world (and Europe in particular) during the Middle Ages comes from the records of Byzantine scholars, which were detailing the Empire's interactions.