Xanatos, Bogarus is not lying because I am Jomon
Moreover, Bogarus does not have the ability to grant you ownership for any Gath's former provinces since Bogarus has an alliance with me, Jomon, to
1 - defeat Gath and to share his provinces
2 - once done with Gath, to attack you.
If you had some trade with Bogarus I had not been aware of, you shall clarify your mutual positions but Jomon won't pay for these occult trades between Bogarus & R'lyeh.
As for Jomon, the situation is quite simple : the war against Gath has been costly and hard. I had to defend, then regain my provinces with heavy losses. In the process, my net benefit is 4 provinces... R'lyeh easily occupied 10+ undefended provinces while we were sieging the last forces from Gath.
Obviously, Jomon can't accept this. Neither can I accept your dominion spreading deeply in my provinces as it is presently doing. I just can repeat my former assertion : peace is possible if you withdraw in your sea and destroy enough temples to keep your dominion pression reasonable. Otherwise, Jomon has no other choice but war.