Suggestion for the fallen empire, which is actually four different political spheres.
The red area is the main part of the empire, a sort of Phoenicia-Sumeria-Indus Valley area where wheat is domesticated, and city states and empires form, but they don't actually have many of their own resources, leading to widespread trade for both metal ore and spices.
They trade with the green, sort of "Celtic tribal" area which has copper, tin, and iron mines, to actually allow their Bronze age to occur. The green area is not owned by the empire, but the chiefdoms there fight over the rights to trade with the advanced eastern civilization.
The blue area grows spices, which starts this world's "Indian Ocean trade", and these spices are traded by the upper classes throughout the world. This area has its own alliance of trading city states.
The yellow area is a separate empire which borrows many of the early civilization aspects (wheat, the wheel, etc.) from the red area, but then invents writing independently and also domesticates another major crop, creating another cultural sphere. They have to trade for spices indirectly through the red area.
This state of affairs is destroyed by an interglacial period, or a massive volcanic eruption that launches dust in the atmosphere, so many of the details are lost to later civilizations. However some of the bronze age technology, and ruins of pyramids and roads, survive, as well as the memory of trade with faraway countries.
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