Glorantha in the God Time progressed from a Green Age to a Golden Age to a Storm Age and then to its near destruction in the Great Darkness. Mortals experienced this as well, and if anyone was curious, here’s some thoughts about that:
Green Age: no need for shelter. Humanity was provided for by the goddess’ bounty.
Golden Age: towns and cities that displayed status. No real fortifications (walls show status and importance, not military defense) since there is no real war. A Solar Emperor (be it Muharzarm, Yelm, the Emperor, Ehilm, whoever) is widely acknowledged as the Ruler of This World, and the rulers of cities are gods or demigods. Humanity serves the gods and there might not really be different “cultures” beyond the gods they serve (so Nochet has an “Earth culture” because it serves Ernalda and her sisters, etc).
Storm Age: towns and cities need fortification as the war between the Gods is reflected amongst mortals. Demigods rule many of these settlements, although some are ruled by mortals descended from the gods. The universal Solar Empire is shattered when Orlanth and the Rebel Gods kill the Emperor (whoever that is). Various rebel gods claim large swaths of the former unity, with Orlanth and his family claiming the most. Some areas remain under the protection of the surviving Fire/Sky gods. This is the era of different cultures. Mortals from one city discover they can no longer even understand people from another city. Unity is lost, replaced by war and politics.
Picture is a reconstruction of the 17th century archaeological site of Arkaim.