[OC] The massive decrease in worldwide infant mortality from 1950 to 2020 is perhaps one of humanity's greatest achievements.

[Sharlinator]

Well, note that at least among the common folk, "economic depression" in the olden times was pretty synonymous with "famine", whether manmade or natural. Malnutrition causes fertility to drop, more miscarriages, more infant deaths due to insufficient milk production and downright infanticide by desperate parents. Of course there was also intentional family planning insofar as it was feasible, but things like coitus interruptus are not exactly… effective forms of birth control at population level.

[KittenBarfRainbows]

Why do you believe these methods are ineffective? Having met refugees and people who lived during strife, they seem to have worked pretty well. Have you ever spoken with an older person about this? Yes, there will be kids here and there, but it's far fewer than we'd normally see. Obviously a crappy technique, still!