I have often wondered this very thing when reading some of the population numbers in the Bible. For instance, the enslaved Hebrew Exodus population was supposedly 600,000 men plus their families. This takes the number upwards of over a million and a half people to almost 2 million people. It's been estimated that Egypt's population was around 5 million people (I can't remember where I read this, sorry) so this means that the population of the slaves was around 1/3 of the population.

There is zero evidence of the Exodus, it's a national foundation myth written centuries later but the number of people the Bible alledges were killed in battles or living in cities seems to be highly embellished. Population studies are hard to come by when trying to compare these old stories to realistic population numbers.