Final answer:
Ghana's trans-Saharan trade thrived, primarily due to the Islamic world's influence to the north, which fostered extensive trading networks across the Sahara.
Step-by-step explanation:
Most of Ghana's trade crossed the Sahara because trade mostly came from the Islamic world to the north. The emergence of powerful West African empires like Ghana and the rise of Muslim states in North Africa facilitated trans-Saharan trade. Shared religious beliefs and cultural practices under Islam, combined with advances in transportation, helped to unify and expand trade across the desert. This resulted in a flourishing trade system, where gold, salt, and other goods were exchanged between West Africa, the Middle East, and Europe, thus making the Saharan route a vital connection between these regions.