I think the history of Gojoseon is the biggest mystery

I've been studying history as a hobby lately,
and the nation of Gojoseon itself is a true mystery.
First of all, there aren't many records available,
and the existing Chinese historical sources are mostly written from the perspective of having conquered Gojoseon (though, of course, they must be taken with a grain of salt).
It just looks like a state located in the Liaodong/Korean Peninsula region.
It used to be said that during the Goryeo Dynasty, Gojoseon was forcibly brought into the narrative to claim national legitimacy,
but seeing how the facts are gradually being revealed—with Goguryeo, Baekje, and Silla all claiming to be descendants of Gojoseon—
it seems there was already a sense of succession regarding Gojoseon even in those eras.
Furthermore, seeing how China continues to refer to the Liaodong/Korean Peninsula lands as (ancient) Joseon territory,
it feels like it must have been a powerful ancient state. It's a shame that research is being hindered due to China's Northeast Project and North Korea.
I'm also curious as to why dolmens are so heavily concentrated in the Liaodong/Korean Peninsula region.