Noone really know the concrete circumstances of the earliest great kingdoms, as much of the political activity in the cradle is shrouded in the veils of the past. Most of the cultural and political developments were underseen without proper notation if any at all; and most of the scripture that has been found is untranslatable due to a lack of comparable texts and therefore a complete lack of alphabetical comprehension. What is however lucky is that the oldest known historical source - the Thricia of Thraches - was written in Old Thrachesian, a language whose scriptures have been well-preserved and thoroughly translated by a few scholars.
Although very vague and semi-legendary (its introduction is basically pagan cosmology), it is of massive importance to the understanding of the political (and definitely military) movements of ancient civilization. It mentions a number of kings in faraway Sivetis that were unified through a mythical Nasetis, the "King of Great Sands", who supposedly came from the West. His reign brought about a "just law under the eye of God" and saw the emigration of soon-to-be Thlayllians and Thrachesians that gave birth to the cultural flourishing of this ancient cradle.
The actual presence of the described Sivete Empire is mostly debunked by historians this day, but still widely debated as some kind of early transpolitan political structure probably existed in ancient Sivetis. Trade flourished as shipbuilding advanced and caravan envoys came with slaves and horses from the Far West. The Thricia itself mentions this as it recites a number of stories of strange men coming with fermented honey from the Far West to Sivetis, and therefore Thrachesia - this being one of the earliest beverages that were supposedly enjoyed by city nobility (including a quite disturbing story of a king being seduced by his slave girl in return for his hand; later she has him beheaded and marries his son).
The Thricia mentions almost nothing of the Illyans and only mentions the Copper River indirectly briefly (“And within the deep north a vein of war is buried within the Earth”
but has plenty of notes on how the supposed rise of Thraches happened. According to the Thricia, when the first settlers arrived to Thrachesia, they found several crumbling, burning cities that were in war with the titans. The exact nature of the proto-Thrachesian river civilization is unknown to this day. According to archeological findings, they were sophisticated craftsmen and potters and traded with southeastern cultures outside the cradle, if one isn’t to be confused by the numerous delicate ivory statuettes of their burial sites. The Thricia’s account states they were mostly gone by the time the Sivetes arrived, but findings of skeletons with destroyed limbs next to weapons as well as a rapid increase of Sivete and Thlayllian artefacts hints that the clash of these civilizations were by no means peaceful.
Regardless of all this, the Thricia was most probably a tool of entertaining storytelling and perhaps even political propaganda. Most of its contents is about the glorification of the supposed Sivete Empire and the legitimization of power that Thraches - its succesors - would therefore have. But while the Thrachesians spread throughout the river delta, the city Thraches itself, while the namesake of the culture, eventually declined into a backwater city state with grand claims but little actual power.
No epics with respectable support for their contents have ever been found about the northern sea and its cultures. However, through archeology, it’s widely known that the Copper River peoples rose to civilization about the same time the Thlayllians did. The explanation is usually that bronze working was developed in Sivetis first and then transported north with trade. The rich metal veins in the Copper River’s soil gave great opportunities for warfare and several early kingdoms rose very quickly after the arrival of bronze working. The opportunities of the land and its cities drew several cultures into the realm, pillaging the wealth of old establishments while installing themselves as kings, and eventually, the land was a patchwork of three main ethnic groups, the Akars, Goraksats and Sabuts. With the great wealth of the river, however, and the easy access to bronze, an early coinage was soon instilled and masses of goods, especially weapons, were exported eastwards to Illyans by sea or southwards to the Thlayllians by land, weaving the fate of the Copper River into the affairs of most foreign city states. Three major Copper River players are relevant to mention at this time: the mercantile Kethesh contesting for dominance over river trade by its geographical location as overseeing river boats; the wealthy Das Dalar who produced the most copper of all the cities; and the mighty upriver Gurakdut who would be the first grand invaders of the river due to their massive military strength and their infamous chariot armies. The Illyans to the east are even less chronicled, but saw a rapidly growing seafaring culture under Ithun’s violent control of trade; a trend which slowly declined as the Lyllas Thallassocracy rose to power with a strategic alliance with neighbouring Tagras and by bridging trade from the archipelago to the northern colonies.
