Diplomacy has essentially become a survival tool for the Byzantine (or Eastern Roman) Empire because they had weaker military capacity in comparison to its neighbours; and as a result, it was not able to establish its hegemonic influence in its surrounding regions. Thus, while one of the goals of diplomacy in the Byzantine Empire was to impress its neighbours, another goal was to prevent cooperation of neighbours against the Byzantine Empire by keeping them in conflict with each other. The Byzantine Empire had weak military power. That's why they tried to impress their neighbours and prevent the cooperation. They couldn't use the diplomacy to strengthen their military power. Instead of expansion or establishing hegemonic influence and having strong military power, they tried to keep their neighbours around and stop ant kind of coopearation against them.