A. A shooting war with someone (China?) or some global apocalypse where men are needed for survival.

B. Marriage and birth rates fall to the level where men are needed to sustain economic prosperity.

C. A majority of people gradually recognize that systemic injustices against men hurt everyone and quit letting feminism drive the train.

D. It does not end. Men become feminized and women continue to complain about both the patriarchy and the absence of competent and manly men to marry. Many women and men never marry; polygamy becomes legal. The West slowly declines.

E. Other?