Societal criminalization of sex with people less than 18 or 17 of old has definitely reduced birth rates.
8 year olds used to find gainful employment. By 15 or 16, these "children" were relatively self sufficient. Now, such jobs are called child labor.
Compulsory mass schooling has also pushed the average child bearing age to 30s.
Health:
Slashing infantile mortality rates has also stopped people from hedging with 5 or more children.
I don't how people perceived contraceptives in the past. However, the lowly condom has prevented lots of pregnancy.
Financial:
Cost of raising a child has sky rocketed. Child birth cost is just crazy. Cost of schooling / rearing - live time cost of a child is something people now seriously debated before giving birth. And having to change houses, and cars to accommodate the growing family is also a thing.
In undeveloped countries with poor health care, low education, child care... high birth rates is still common.
Japan 2d partners:
What's up with that country? Seems like they just became uninterested in actually having sex with actual human beings.
If having sex with animals is bestiality; having sex with dead people is necrophilia; what is sex with 2d anime girls?