- [Narrator] Rapa Nui, also known as Easter Island.

This tiny little island in the South Pacific is world-famous for one thing, the moai.

- The moai building has often been portrayed as some kind of frenzy, as some kind of competition between different clan groups where lots of trees were cut down in order to construct and to transport the moai.

- [Narrator] According to this view, moai building deforested the island.

The soil was starved of nutrients, leaving a barren rock-strewn land.

Then, this theory goes, things got worse.

- The scarcity of resources resulted in a societal collapse.

The island erupted into intertribal warfare and led to a very impoverished population living on a barren island.

- [Narrator] The true story of Rapa Nui is one of survival against the odds by an ingenious and resilient people who came to a bad land and made it good.

Looking at all the archeological evidence, it seems more likely that rather than a self-inflicted ecocide, the true collapse of Rapa Nui society was caused by outside influences.

- As time went on and the evidence accumulated, we realized that a lot of what people thought was collapse was something that actually happened after Europeans arrived and it had an entirely different cause, and that was the introduction of Old World disease.

- There was the smallpox, there was the Spanish flu, leprosy, slave trading.

It was difficult to live here, and it was more difficult to keep the social structures and the life as the way that we knew it.

- [Interviewee] Over time, we see people sort of abandoning ahu and moai.

It's a loss of population.

There're just fewer people because of the effects of diseases.

So people are not attending to the ahu and rebuilding them in the way that they did in the past.

- [Narrator] Things got even worse in the 1860s.

- Peruvian slave traders captured about a third of the population on the island and forced them onto their ships to work in Peru.

(interviewee speaking in French) - [Interpreter] There were protests, even the Vatican got involved, and consequently, the companies were forced to return the inhabitants to the islands.

However, these people had contracted smallpox on the American continent.

Only 15 people made it home, and this was enough for an epidemic of smallpox to break out there.

(interviewee speaking in French) - [Narrator] By the time it was over, there were less than 200 Rapa Nui left alive.

(suspenseful music)