As elaborated earlier, diplomatic practices and interaction did exist among political entities even in ancient times elsewhere in the world. Yet, the content of these diplomatic practices were far from being a model for modern diplomatic customs. The biggest obstacle for cultivation of a systematic diplomatic custom was, of course, the issue of continuity. Diplomatic interactions of the ancient world were built upon quite an intermittent structure and shaped in an issue-specific manner. They did play a role in the formation of customs in the field of trade and crystallization of the borders. Yet, the modern diplomacy, which required continuity and constant contact, emerged in the Renaissance Italy. The content of the diplomatic practices in the Renaissance Italy focused mainly on long term alliances, customs union, and defense against the intervention that would potentially come from non-Italian Europe. The correct answer is D.