Depending on my game and civilization build, I often get approached by the AI to forge an alliance, but - as most 4X games have taught me - these alliances are more trouble than they are worth so I reject them 99.999999 percent of the time (in fact in MOO2 I don't think I've ever done an alliance only a non-aggression treaty).

So my question is for you players who play on Average difficulty and up: is there *ever* a reason to enter into an alliance? The only reason I can think of is to secure a border while seeking to expand into another AI's territory, other then that, I don't see a purpose.

Thanks in advance

BoP

Good points all around. Definitely something to keep in mind for future reference.

Thank you!

The other downside is that your ally can then expand into your territory. Even if you don't plan on betraying them, it can be a real pain when they steal one of your best worlds.

True, but you can do the same to them :)

Plus I think non-allies can colonize planets in one of your systems without triggering a war ... but an ally can do it deep your territory since they can use your bases just as you can use theirs

The first and most obvious benefit is, as has been mentioned, fleet range. This might come in handy if you're planning to strike or retaliate on an enemy with Deuterium fuel cells. Even more importantly, this allows for more diplomatic contacts early in the game.

The other benefits of alliances are for diplomacy-attuned races. Firstly, alliances win you a near-guaranteed pack of votes at the Galactic Council, so focusing at forging alliances gives you a fair chance to win the very first elections. Secondly — and this is more subtle — you can subdue allies' aggression. Computer-controlled races eagerly respond to "make peace with…" demands. As a direct consequence, your allied block wages less wars and becomes notably stronger over time while the other part of the galaxy is typically drowning in turmoil. Keep in mind, that the computers are highly unwilling to declare wars on yur mark, so just waiting for the "correct" war to emerge is the best strategy.

Someone could change their tag line from 'new user' to 'necromancer' but still, good finer points, some new to me. ;-)

Your allies will vote for you during a galactic council session (unless they themselves are up for election). So, if you have enough systems to be eligible to stand for election in the council, you can gain an early win by diplomatic victory if together you and your allies control 2/3 of the votes.

I've also experienced that having an extremely high relations bar (ie. practically maxed-out) makes the aliens quite agreeable when demanding that they give you their technology ;)

EDIT: I see Kmickle already beat me to it.

Small correction: It is the amount of population, not the number of planets, that decides how many votes each one gets.