The left hand of darkness

Le Guin's Hainish series begins with the assumption that centuries ago humanoids from the planet Hain ventured through the solar system establishing colonies on various planets including Earth. For mysterious reasons these colonies lose all contact and knowledge of each other until the 21st century when an attempt is made to establish a galactic league. Individual stories in this loosely organized series explore the inherent communication difficulties in the mingling and clash of cultures that, over the centuries of separation, have developed widely disparate social and political structures as well as a range of biological differences