Actually, Yan dynasty could have done many policies that would have pacified the people of the Songnu and the Sirong tribe.
If they were allowed to assimilate without changing too much of the Songnu and Sirong tribe and without having to acknowledge the superiority of the Yan people then they could have become a strong force that the Yan could use to fight against the tribe of the Steppe
But the Yan people believe any race that is not Yan would have different hearts than them. And they could not trust outsider at all.
And it is precisely because they could not trust outsider, that they could not win the loyalty of these tribes.
They always lamented that the people of the jungles and mountain could not be loyal but they never examined themselves and think why does the people of those tribes, that are not Yan could not be loyal to them
How could you be loyal to a government that will always treat you like an outsider, and give you insulting names