Birth control is not the overwhelming #1 issue other than at the tail end. TFR plummeted continually from from 1800 to 1920 (from 7 to 3) in the US (https://www.statista.com/statistics/1033027/fertility-rate-u...).

The primary issues were first increased probability of survival to adulthood (shift focus to raising fewer kids better) and then higher opportunity cost (especially for women who gained opportunities).