It is said that after the fall of Goguryeo, an independent nation called Sogoguryeo existed in what is now the Liaodong Peninsula.
However, there is no clear evidence that it existed, so it is only a ‘rumor’ so far.
According to the Chinese history book
In order to reduce opposition from the locals, Godeokmu, the son of King Bojang, was appointed as a local governor.
However, as the Tang Dynasty gradually became confused, Godeokmu created a country called Goryeo.
(At the time, it was called Goryeo, and academic circles called it Sogoguryeo to distinguish it from Goguryeo.)
This theory originated from a Japanese scholar, but it is not currently accepted as an established theory because there is no solid evidence.