#1 A meteor hit the Earth. The virus from the meteor turns every woman into shemales and every man into a submissive slave. Then a big war between them destroys nearly everything. The rest of humanity build a massive city for the shemales and the shemale queen. Only a thousand woman did not turn into shemale, but every shemales and man are fertile, and nobody can impregnate them. You are the only one who managed to survive everything, and you are the last hope of humanity.
#2