During the Bronze Age collapse, cities in the Near East, North Africa, and Eastern Mediterranean imploded in violence and mystery. Historians now theorize why these civilizations, along with their knowledge and culture, fell so suddenly nearly 4,000 years ago.

In its heyday, the “Bronze age civilization” was a happy and prosperous time, defined by a population that produced bronze by smelting copper and alloying it with tin, arsenic, or other metals. The strength of bronze over other metals meant these civilizations had a technological edge in weaponry, engineering, and other industries.

The citizens of this era built large urban communities, developed complicated social classes, invented a variety of writing systems, and were interconnected through trade and migration. But around 1177 BCE, this sophisticated network went down in flames, leaving clues for future theories.

One popular and controversial hypothesis is that these civilizations were wiped out by invaders, more specifically, an army of “Sea Peoples.” Because there are no artifacts or written records that identify the origins of these raiders, many believe the group is a combination of the many different nomadic populations that traveled the eastern Mediterranean.

Others argue that the demise of the Bronze Age was largely one of self-destruction. This theory suggests that while sophisticated, these cultures’ political systems were corrupt, leading to inequality and social instability.

Finally, a 2013 study of pollen grains and sediments from an ancient lake in the region found evidence of climate changes around the end of the Bronze age. Researchers believe that this led to a combination of droughts, food shortages, mass migration, and social unrest, all of which left the region vulnerable to predators (perhaps the Sea Peoples) and eventual collapse.

We may never know whether these cultures fell because of one of the reasons outlined above, a combination of them, or something else altogether. It’s also easy to draw parallels between the social unrest and climate conditions of the Bronze Age and today.

For these reasons and more, it’s important to heed what they say about history – learn from it or be doomed to repeat it.