[Arkcon]

Originally posted by Suicide Junkie:

The best questions:
Would you Surrender to him if your positions were reversed?
After years of war with positions reversed, would you trust him to not use the treaty to bypass your remaining defenses and slaughter your people?

Along those lines, you said you had other races to worry about. Maybe the AI stubborness is there to provide a challange. You've beaten them to submission, now when you turn your back, they grow to become a threat again.