Mexican President Andrés Manuel López Obrador speaks during his daily morning press conference at the National Palace in Mexico City on March 26th, 2019. (Photo: Pedro Pardo/AFP/Getty Images)

On Monday, the president of Mexico announced that he had sent a formal letter to the king of Spain, asking the monarch to acknowledge and apologize for Spain's conquest of Mexico.

In a video released on social media on Monday, Andrés Manuel López Obrador, Mexico's president, stood next to his wife in front of the ruins of a Mayan pyramid in Tabasco, one of the country's southernmost states. Speaking to the camera, AMLO (as he is known in Mexico) explained that he and his wife had come to Centla—the Maya city whose ruins they stood among—to commemorate the 500th anniversary of the the battle the Chontal Maya fought against the forces of Spanish conquistador Hernán Cortés.

"There were massacres and oppression," AMLO says in the video. "The so-called conquest was fought with the sword and the cross. They built their churches on top of the temples." He then called on Spain to apologize for its role in the conquest, and to ask for forgiveness from Mexico's indigenous peoples.

Spain immediately rejected AMLO's demand for an apology. In a statement issued on Monday, the government of Prime Minister Pedro Sánchez wrote:

The Spanish government profoundly regrets the publication of the Mexican president's letter to his majesty the king on March 1st and completely rejects its content. The arrival of the Spanish on Mexican soil 500 years ago cannot be judged in the light of contemporary considerations. Our closely related peoples have always known how to view our shared history without anger and from a shared perspective, as free peoples with a common heritage and an extraordinary future.

This November will mark the 500th anniversary of the day the Aztec king Montezuma invited Cortés and his soldiers into Tenochtitlán, the Aztec capital which was—with a population of 200,000—one of the largest metropolises in the world at the time. Though the Aztec greeted Cortés peacefully, the conquistador went on to besiege the city for 75 days, causing a famine that decimated the population. Cortés went on to level Tenochtitlán and begin building the Spanish colonial seat that would become Mexico City.

After seizing control of the Aztec empire, the Spaniards quickly conquered the rest of what is modern-day Mexico, establishing an iron-fisted rule by 1525. Seeking to extract gold and other resources from their new colony, the Spaniards created the encomienda system, which was, in essence, a way of organizing plantation-style slavery to force indigenous people to labor in the mines and fields. For generations, indigenous people who survived the plague of European diseases worked as slaves, as the Spanish missionaries forced them to adopt Christianity and abandon many of their native customs.

One of the most famous accounts of Spanish brutality comes from one of these missionaries. Bartolomé de las Casas, a Domincan friar, wrote about his experiences traveling through Spain's colonies in Latin America and the Caribbean between 1517 in 1540 in his book, Brevísima relación de la destrucción de las Indias (A Short Account of the Destruction of the Indies). Las Casas described the systematic torture, rape, and mutilation the Spaniards exacted on indigenous people in every colony he visited.

"Their reason for killing and destroying such an infinite number of souls is that the Christians have an ultimate aim, which is to acquire gold, and to swell themselves with riches," Las Casas wrote.

The Oxford Encyclopedia of Human Rights calls Spain's invasion of the Americas the first large-scale genocide of the modern era. In the land that became Spanish colonies, at least eight million indigenous people were killed by Spanish massacres and European diseases. Across two continents, up to 95 percent of all people were killed.

In contrast to the Spanish government's reaction to AMLO's request, Spain recently apologized for another historical crime of a similar age: In 2015, Spain's parliament approved a law creating a path to citizenship for Sephardic Jews whose ancestors were expelled from Spain in 1492.