The Portuguese had a head start in the Age of Discovery. Soon they had laid claim to all of the western coast of Africa. This blocked Spain (Europe's biggest country) from the gold of Africa.
What were they to do? In 1492 a captain from Genoa (Italy) went to the Spanish king and suggested they tried to go west, across the vast Atlantic Ocean. He said that way the Spanish could get to China and the Spice Islands directly. But no one had done it before.
