I have convinced Hard AI to ally with me for the specified time limits, but only by offering them absurdly high amounts of credits and resources and the occasional planet. Having played Sins one for..a decade, I took the time to figure out the new game has a similar but semi functional at best system. After you bribe your partner, you can get him to guard or attack planets to some extent, but i found the amount required to onboard an AI to be too staggering for diplomacy to be practical or fun in the early to mid game. I have also noted that it was impossible to score late game allies with Hard+ AI players, likely because player faction points from the old Sins are baked in but inaccessible to human players to improve via missions or research.
Sins1 Diplomacy is vastly superior in functionality. I am disappointed that this is not a base part of Sins2.
It is worth noting that you can give any player faction resources, credits, and even planets, however. This is somewhat handy when your AI enemies are duking it out and you would prefer them to have a prolonged campaign against each other while you navigate the match unmolested.
