In most games I've had, the races tend to ally with everybody, creating a deadlock on bieng able to declare war. In my last game, I had all victories except conquest victory disabled, on normal difficulty (which I generally play on), and large galaxy. Even though there were some wars early on, later the other civs started allying with each other and this really ended up bieng to my advantage because with everybody in one huge alliance, nobody was able to declare war on each other. Sure there was that 'disgruntled worker kills alien leader, now the _____ declared war on us' type event one or two times, both times I was able to buy my way out, but it was to my advantage since I decided to switch to cultural assimilation and with the one big happy family of an alliance, the influence wouldn't piss off the others (I did keep my military rating up though just in case). It took many years, but they all (I started out with all 9 races, 4 of them were conquered in wars, the rest were eventually assimilated by me, and I was playing the Torians) fell to my cultural assimilation process one at a time.

My point bieng is that the races do alliances too much and in my case, doing alliances with everybody just ended up 100% to my advantage because only conquest victory was enabled. So, the amount that they ally with each other needs to be looked at because the AI needs to consider the victories available and with just conquest victory, it makes no sense to do one massive alliance. While that could be called an exploit, I simply took advantage of the opportunity that had developed.