if you learn about history the one reduce massive human population
1.war
2. natural disaster
3. harsh environment
of course human population limiter is harsh environment, at the top chart.
example antartic environment etc
funny
the variety disease itself become varry because interaction of foreigner.
human certain places too had their own unique immunity.
disease plaque never limiting number because it never answer western low growth rating
it onnly REDUCE NOT LIMITING and rarely significant because OFF TOPIC ...!!!
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summary because not having proper knowledge of sophisticated medicine is absurd to think could limit human population to below 1 billion