The Age of Discovery is an informal and loosely defined European historical period from the 15th century to the 18th century, marking the time in which extensive overseas exploration emerged as a powerful factor in European culture. Many lands previously unknown to Europeans were "discovered" during this period, though most were already inhabited and from the perspective of many non-Europeans it was marked the arrival of settlers and invaders from a previously unknown continent. Global exploration started with the Portuguese discovery of the Atlantic archipelago of the Azores, the western coast of Africa, and discovery of the ocean route to the East in 1498, and the trans-atlantic ocean discovery of the Americas on behalf of the Crown of Castile (Spain) in 1492. These expeditions led to numerous naval expeditions across the Atlantic, Indian and Pacific oceans, and land expeditions in the Americas, Asia, Africa, and Australia that continued into the late 19th century, and ended with the exploration of the polar regions in the 20th century.