La mano sinistra delle tenebre by Ursula K. Le Guin

Genly and the Ekumen wonder whether the harsh climate, the androgynous nature of the inhabitants, or other factors can account for the absence of war. One notable feature of Gethen is that its nation states have never gone to war. Gethen has two major nation states: Karhide and Orgoreyn. Its level of technology is roughly equivalent to that of early 20th century Earth, but with some anomalous differences - although no forms of air transport (dirigibles or airplanes) have been invented and the most advance form of communication is radio, the Gethenians have developed relatively advanced sonic weapons. Gethen is an extremely cold planet, and is nicknamed 'Winter'. Thus each individual can both sire and bear children. The inhabitants of Gethen are sequentially hermaphroditic humans for twenty-four days of each twenty-six day lunar cycle they are sexually latent androgynes, and for the remaining two days (kemmer) are male or female, as determined by pheromonal negotiation with an interested sex partner.

Once contact has been successfully established and the new world agrees to join the Ekumen, the First Mobile is replaced by a permanent mission, led by a Stabile. In an effort to minimise the effects of culture shock, Ekumen policy dictates that newly-rediscovered worlds should first be secretly observed from space and the approached by a roving individual envoy, the First Mobile. Eventually, a new and more egalitarian social order, the Ekumen, arises in its place, and begins to reach out to former outposts of the Empire. Following the demise of the empire, many outlying colonies like Gethen become isolated, losing any record or social memory of their former contact with Hainish culture.

The backstory to Le Guin's Hainish cycle is founded in the concept of the expansion of human culture through the galaxy, thanks to the development of near-light-speed travel, which in turns leads to the rise and eventual collapse of a Galactic Empire. The Left Hand of Darkness is the account of the efforts of a man named Genly Ai, a representative from a galactic federation of worlds (the Ekumen), who seeks to bring the world of Gethen into that society.

La mano sinistra delle tenebre by Ursula K. Le Guin