The Utopian "Herland" Trilogy

Three young American men discover a country inhabited solely by women, who reproduced by parthenogenesis (a form of asexual reproduction), and had borne only girl children for two thousand years; eventually they marry three of the women.
The central theme of Herland is defining gender — the roles, how it is socially constructed, and how it is viewed as unchangeable by both genders. It also focuses on motherhood and individuality.