Robert, the Son of God, can fully understand that his only choice now is to cooperate well with the Alliance.
To acknowledge the Alliance as part of the Empire, part of humanity, and recognize Gu Hang, the High Lord and governor of the Dark Side of the Empire. Furthermore, he needs to rely on the Alliance, which is performing quite well on the Dark Side of the Empire, to continue their expedition and unify the Dark Side.
Additionally, he hopes the Alliance can provide support to help him initiate an expedition on the Holy Territory of the Empire, similar to the Dark Side Expedition.
Ultimately, to restore peace across the entire Human Empire.
Of course, true peace is impossible. Although it is the wish of the Son of God, he knows rationally that it is unrealistic for every place to be absolutely peaceful.
