Final answer:
European nations sought a new route for the silk and spice trades in the 15th century because the fall of Constantinople disrupted the traditional overland routes, leading to increased costs and risks. Religious motivations and technological advances in navigation also spurred the search for new maritime trade routes, marking the onset of the Age of Exploration.
Step-by-step explanation:
In the mid-15th century, European nations required a new trade route for silk and spices primarily due to geopolitical changes and economic factors. The fall of Constantinople in 1453 to the Ottoman Empire significantly disrupted existing overland routes, like the Silk Road, which Europeans had used for centuries to trade with Asia. These routes became controlled by Muslim middlemen who levied heavy taxes, making the trade more costly and impractical. In addition, the end of the Pax Mongolica led to increased risks and costs on the overland routes.
Another contributory factor was the zeal for religious expansion. Nations such as Spain and Portugal, motivated by a desire to spread Christianity and a sense of competition with Muslim traders, financed voyages to discover oceanic routes to Asia. This led to the Age of Exploration, directly impacting global trade, politics, and the start of the colonial era. Innovations in sailing technology, including the lateen sail and the magnetic compass, equipped explorers to embark on maritime voyages that eventually established new trade routes to the East and to the Americas.