despite its name, only a small part of the territories is covered by actual forest: the eastern part, which is claimed by thunderclan and their hunting grounds. the rest are hills, grasslands and marshes. a river, named river chell, cuts through the region, making up a border between riverclan and their neighbours, thunderclan and windclan. a thunderpath, named windover road by twolegs, makes up the border between shadowclan and thunderclan.

in the beginning, the region was a wilderness without predators or human living nearby, and after some time, cats arrived in small groups and began to settle down. however, they didn't set up borders, and their territories overlapped — resulting in lots of battles and bloodshed.

after a particularly ferocious battle, the survivors were confronted by the spirits of their fallen companions, urging them to unite and live in peace.

however, the cats could not agree on who would lead them, so five cats: thunder, tall shadow, river ripple, wind runner, and clear sky, each demanded to be leaders. they decided to split into five groups in the end: and others chose to follow a leader who was best suited for them as an individual.

they developed the warrior code, and founded the five clans — thunderclan, shadowclan, skyclan, riverclan and windclan. they divided their hunting grounds between themselves, adapting to the conditions that reigned on their territories. the spirits of the fallen cats made up starclan: ancestors who guided the living with advice.

twolegs arrived soon, constructing a thunderpath that made up the border between thunderclan and shadowclan, then built a twoleg place which forced skyclan to leave their territory, the other four remaining clans stayed.

( all information was found off of
the warriors wiki on google. some
information may have been
removed, tweaked or added )