an actual solution would have to include deurbanization on a large scale. none of the other factors besides maybe contraception is as important. fertility was plummeting in the soviet union before the curtain fell so the root isn't capitalism. fertility in kolkatta, one of the poorst regions in the world is lower than in germany so education of women, wealth or feminism doesn't play such a big role. the common denominator in every country is that the economy organises the people to live densely together so the exchange of goods and services becomes easier. at the same time for some reason this makes have less children. as a rule of thumb the higher the population density the less children people will have. that is also why immigrants adapt to local fertility rates. if we don't find a way to organise our economies differently it will collapse eventually.
Germany