The Portuguese believed they could find an easier sea route to Asia due to a mix of economic incentives, technological advances, and strategic necessities that made overland paths increasingly untenable.

Blocked Trade Routes

Muslim and Venetian middlemen dominated the Silk Road and overland spice trade, imposing high markups on goods like pepper, cloves, and silk reaching Europe. Controlling the Mediterranean and Red Sea, these intermediaries blocked direct European access, inflating costs and limiting profits for nations like Portugal.

Technological Innovations

Portuguese shipbuilders developed the caravel, a nimble vessel ideal for long ocean voyages with lateen sails for wind efficiency and better navigation tools like the astrolabe and compass. Prince Henry the Navigator's sponsorship from the 1410s onward mapped Africa's coast, proving ships could round the continent southward rather than risk unproven western routes. Early successes, like bypassing the Sahara by sea for gold and slaves, built confidence in an all-water path to India.

Economic and Religious Drive

Spices preserved food and fueled medicine/perfumery markets, promising vast riches without intermediaries—Vasco da Gama's 1498 voyage to Calicut validated this by slashing transport costs. National pride and crusading zeal under kings like John II motivated bypassing "infidel" lands, establishing forts from Goa to Malacca for dominance.

TL;DR: Blocked routes, superior ships, and spice profits convinced Portugal an African coastal path was feasible and superior to land caravans or risky alternatives.

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