I think its kind of like reality show contestant behavior. Teaming up for now , but , knowing we will have to compete against each other later. It plays into my "the AI thinks its people" belief. The AI doesn't "think" its leading a virtual nation or empire ,but , "thinks" its playing a game , and , will do what it can to win. The AI will "want" to pit you against other civ's to wear down your army ,when it backfires and leaves you with a larger stronger empire , the civ that you started the war for soon turns on you ,because , you now look like bigger competition.