Final answer:
Trade became the primary driver of contacts in Ethiopia and the Horn of Africa due to the settlement of Arab merchants, the growing Indian Ocean trade, and the intensification of trans-Saharan trade networks.
Step-by-step explanation:
Contacts between peoples and polities in Ethiopia and the Horn of Africa became primarily driven by trade due to several historical developments. First, the Arab Muslim merchants settled in the region and intermarried with the Bantu peoples, establishing firm commercial contacts. Second, the Indian Ocean trade network flourished with the spread of Islam and the creation of trade-based societies that connected East Africa to Middle East and Asian markets. Finally, the trans-Saharan trade intensified, facilitated by the rise of empires like Ghana and the unification under Islam, creating vast networks that handled commodities like gold, salt, and slaves. The Indian Ocean trade, coupled with the cultural significance of East Africa, expanded the economic and cultural contacts in the region. Wealth accumulation through trade led to the growth of city-states into kingdoms and empires, fostering diplomatic relationships that often superseded warfare.