Before 1453, Europeans had enjoyed relatively easy access to the East. Trade had been going on for centuries between Europe, the Indies (roughly South and East Asia) and China through the Silk Road, a land passage. However, in 1453, with the fall of Constantinople to the Ottoman Turks, tensions between Christians and Muslims rose, and the passage became a lot more restricted and dangerous.
This change motivated Portuguese navigators to try to find another route to the East through the ocean. The first promising strategy was the Cape Route of Bartolomeu Dias in 1488, around South Africa. However, there were other proposals that suggested going west. This is what Christopher Columbus attempted, which led him to discover America. These events led to the beginning of the Age of Exploration, which ended with the exploration of the polar regions in the 20th century.
