Mayan civilization
Between 900 AD and 1000 AD, the cities in the southern lowlands had more and more problems until all the people left. The Maya civilization there stopped making big monuments and carvings. People who study the Maya civilization are not sure why this happened. They have many different ideas - some people think there was a big environmental disaster, or a disease affected a lot of people, or there were just too many people for the amount of food they could grow.