If you want a more developed societies such as middle-ages/ renaissance/ even the beginning of the industrial revolution you can do what Rome and the Chinese empires did. They interfered with the smaller neighbours and created conflicts and played the neighbouring clans against one another. You just have to avoid any person/alien from uniting the fractious clans (races) into one big super clan like Genghis Khan did in Mongolia. Or even more recently, the African National Congress did in overthrowing the Apartheid Nationalist party.