"It seems that although there was almost no contact with the other side, Jiaxia certainly knows that this is a civilization not weaker than the Great Xia Dynasty."
Fu Qingjun has reason to believe that Jiaxia had, at some point, waged war and fought against the top experts of the other side.
And then discovered that the forces were evenly matched, or perhaps won a bitter victory with too large a price...
Then traveled through time, returned to the previous point in time, "resetting the save file", and established national diplomacy, advocating peace. Each used national ambassadors, visited each other, expressed their love for peace, while secretly revealing their national strength to deter others to avoid mutual destruction.
