Final answer:
The Byzantine Empire used diplomacy and alliances to protect its interests. As a Byzantine diplomat, you could try a combination of methods, such as threatening with military retaliation, buying him off, or arranging a marriage to convince the invading chief to stop advancing on Constantinople.
Step-by-step explanation:
The Byzantine Empire was known for its aggressive use of diplomacy to protect its interests. One method of diplomacy was to negotiate treaties and form alliances with foreign powers. Another tactic was to make friends with the enemies of their enemies. The Byzantines also used underhanded tactics, such as supporting exiled foreign royalty to install them on their thrones if it benefited their empire.
In the given scenario, as a Byzantine diplomat, you could try a combination of methods to convince the invading chief to stop advancing on Constantinople. Threatening with military retaliation could be one approach, but it should be used cautiously to avoid further aggression. Offering a bribe or buying him off could also be attempted, but it depends on the chief's motivations and if he can be persuaded by material gains. Arranging a marriage between him and a Byzantine noblewoman could be a way to form an alliance and establish a connection of trust.