11 lost civilizations and how they might have fallen

Sumer Middle East 5000s-2000s BCE Probable cause of demise: Invasion Pictured: U.S. Soldiers climb the steps of the Ziggurat of Ur, a Sumerian monument built during the Early Bronze Age (21st century BC). (Spc. Samantha Ciaramitaro/U.S. Army)

Minoan Southern Europe 2700s-1500s BCE Probable cause of demise: Natural disaster, invasion Pictured: A fresco found at the Minoan site of Knossos, indicating a sport or ritual of "bull leaping", the red skinned figure is a man and the two light skinned figures are women. (Public Domain)

Harappa Indian Subcontinent 3300s-1300s BCE Probable cause of demise: Environmental collapse Pictured: A Harappan coach driver, ~2000 BCE (Miya M.)

Nok Africa 1000s BCE-500s CE Probable cause of demise: Unknown Pictured: Nok sculpture. Terracotta, 6th century BCE–6th century CE, Nigeria. (Federal Republic of Nigeria)

Maya Central America 2600s BCE-900s CE Probable cause of demise: Environmental collapse, overpopulation Pictured: North Acropolis, Tikal, Guatemala. (Public Domain)

Anasazi North America 1200s BCE-1300s CE Probable cause of demise: Environmental collapse, overpopulation Pictured: Remains of multistory dwellings constructed into the side of the canyon wall at Bandelier National Monument in New Mexico. (Public Domain)

Polynesians of the Pitcairn Islands South Pacific 1000s-1400s Probable cause of demise: Invasions, disease Pictured: NASA Satellite Image of Pitcairn Island in the Pacific Ocean. (NASA)

Aztec Central America 1200s-1500s Probable cause of demise: Invasions, disease Pictured: The Aztec Pyramid at St. Cecilia Acatitlan, Mexico State. (Public Domain)

Inca South America 1200s-1572 Probable cause of demise: Disease, overpopulation Pictured: Machu Picchu Temple of the Sun (also named "the watch tower"), located in the Cusco Region of Peru, South America. (Fabricio Guzmán)

Rapa Nui South Pacific 300s-1800s Probable cause of demise: Environmental collapse, overpopulation Pictured: Moai, monolithic human figures carved from rock, at Rano Raraku, Easter Island. (Public Domain)

Beothuk North America 1500s-1829 Probable cause of demise: Invasion, disease Pictured: A Beothuk archaeological site and museum in northeastern Newfoundland. (Carl B.)