What caused the global population decline between 400 and 200 BC?

[septimus]

@tim314

Yep, that explains it. The chart appears to use the McEvedy and Jones estimate for 500 BC and 200 BC, but uses the Biraben estimate for 400 BC. Looking at the estimates individually, neither shows a drop in population for that date range.

This is essentially the same answer I gave when “What happened to the world population less than 2500 years ago?” was asked two years ago.

@septimus

The data in the graph was taken from the lowest estimates in this Census Bureau compilation.

As you can see, the lowest estimators, McEvedy and Jones, simply did not provide an estimate for 400 BC; hence that year shows as anomalously high.