Between July 1519 and September 1521, the Spanish soldier and explorer Hernán Cortés (1485–1547) conquered what is now central and southern Mexico and added it to the globe-spanning Spanish empire. He swiftly toppled the Aztec empire and waged a genocidal campaign, resulting in the deaths of millions. During this time, he sent five extended letters to Emperor Charles V, the ruler of Spain and the Holy Roman Empire. Throughout these letters, Cortés attempted to justify his often-brutal actions.