Generally speaking, birth rate declines happen because people have more things to do than have children. That's why all rich countries experience them and noone

Generally speaking, birth rate declines happen because people have more things to do than have children. That's why all rich countries experience them and noone has been able to reverse them. (Japan actually has slightly reversed theirs. Korea hasn't because Korean men are awful misogynists no women want to associate with.) There are high density countries with high birth rates though; they're either very religious (Israel) or very poor (Africa).