Through exploration and conquest or royal marriage alliances and inheritance, the Spanish Empire expanded to include vast areas in the Americas, islands in the Asia-Pacific area, areas of Italy, cities in Northern Africa, as well as parts of what are now France, Germany, Belgium, Luxembourg, and the Netherlands. The first circumnavigation of the world was carried out in 1519–1521. It was the first empire on which it was said that the sun never set. This was an Age of Discovery, with daring explorations by sea and by land, the opening-up of new trade routes across oceans, conquests and the beginnings of European colonialism. Spanish explorers brought back precious metals, spices, luxuries, and previously unknown plants, and played a leading part in transforming the European understanding of the globe. The cultural efflorescence witnessed during this period is now referred to as the Spanish Golden Age. The expansion of the empire caused immense upheaval in the Americas as the collapse of societies and empires and new diseases from Europe devastated American indigenous populations. The rise of humanism, the Counter-Reformation and new geographical discoveries and conquests raised issues that were addressed by the intellectual movement now known as the School of Salamanca, which developed the first modern theories of what are now known as international law and human rights. Juan Luis Vives was another prominent humanist during this period.