He says: "...that even we were not able to accomplish..."
So I guess the old Great Heavens also desired to unify China.
I think the difference between Renpa and Ouki is that Ouki outright wouldn't fight for a king he didn't deem worthy enough (and that didn't have the specific, true desire to unify China) while Renpa had such lust (like Hyou) for battle that he keeps on waging war regardless. Lol.