>>105512920World pop in the 1200s was halved and took centuries to recover. Ireland's population was massively reduced in the 1800s due to famine and mass emigration (principally to the rest of the UK as it was at that time) and has yet to recover.
There were several unique factors driving population growth in the post-war period which no longer apply today: firstly, the entire planet had been gripped by the second massive war in living memory (between which there had been a number of massive regional conflicts as well as mass pandemics of disease, beginning with the 1918 flu pandemic); this led to grateful survivors starting families and demanding (in many parts of the world, not just the first world) a new political settlement, leading among other things to the post-war boom in births (the so-called "boomers" that the soap eaters are now trying to erase the memory of by repurposing the word), the emancipation of former colonial holdings and a greater interest in keeping accurate records of those countries by their new governments. We don't in fact really know what the population of a lot of countries was, exactly, because censuses were rare and not particularly accurate; this is still true today.
Secondly, that same post-war boom in births and the attendant increase in living standards has led to greater longevity; but greater general education and greater longevity combine to reduce birthrates drastically, an effect masked on raw population numbers by longer-lived cohorts. Birthrates also go down quickly once people realize they're not going to lose 4 in 5 kids before the age of 5 or need them to do manual labor as automation takes hold. In China, for example, the population is likely to fall significantly this century, thanks to those factors and the additional effects of the one-child policy and a cultural bias toward males which has significantly skewed the ratio of male:female.
>>105514573Once. Out of all the times it could have. Just once.