Exchange between christians and muslims in the 15th century

[Antonio the Sixth]

To the extent that it makes sense to think of Islam and Christendom as meaningful political units at that point in time (it really doesn't), unquestionably Islam. Byzantium, even with its glory days long past, remained a major center of culture (while the story of fleeing Byzantines kickstarting the Renaissance was wildly exaggerated, there is some truth to it), religious spiritual power, and historical prestige (witness Russia's subsequent efforts to cast itself as its heir). The Ottoman Empire went on to become one of the foremost world powers for the next 3 centuries. Al Andalus, while culturally rich, had never been of much political significance (hell, in its earlier form it was basically the retirement home for a deposed dynasty of Caliphs). And while Spain would go on to become extremely significant for obvious reasons, I'm pretty sure that some other Atlantic power would have filled its shoes soon enough. Heck, the crowns of Castille and Aragon would still exist even if they'd failed to take Grenada, and they'd still have access to the Atlantic, so nothing would prevent the Columbus expedition from happening. The Reconquista is ultimately a secondary (though by no means minor) historical event.