Pretty much any country that approaches development and has equal rights for women leads to a birth rate bellow replacement level. You don't need to castrate anyone, you give women education, birth control, require dual incomes to effectively survive as a family unit, equal rights and an (semi-)urban lifestyle and it pretty much shakes out to that automatically. Eventually the issue will be to have enough children, and an economic model that that can deal with shrinking old populations without horrific consequences.

There is only 77 countries that are above the replacement rate and it's going down everywhere: https://en.wikipedia.org/wiki/List_of_sovereign_states_and_d...