Impossibly promising grand sci-fi strategy Stellaris continues to intrigue, the latest dev diary (opens in new tab) explaining just how Alliances and Federations are going to work. To cut a long story short, if you're in an Alliance with a bunch of other civs and you want to do a war, you'll need to get the approval of all the other members—so you'd better declare some goals for the war that will benefit your allies too. If your galactic chums don't fancy a war, you can always leave in a huff and make a go of it on your own—alternatively, if things are just peachy between you, maybe you'd like to take things to the next level and form a Federation?
In stark contrast to those votey Alliances, Federations are governed by a single president who can "act with impunity", the sizeable downside being that everyone in a Federation gets a turn at being president. That sounds like a recipe for disaster/hilarity right there. You also can't win a game on your own if you remain part of a Federation: victory is shared between members.
"Another interesting feature of Federations," says Paradox, "is that they have a special joint space navy in addition to the forces of the separate member empires. The Federation president gets to design these ship templates using all the best technologies of all the member empires. The president also gets to control these fleets, of course. As a rule of thumb, several fairly equally matched empires might want to form a Federation, especially in the face of aggressive, significantly larger neighbors, but it might not be the best idea for empires who are dominant in their own right. Of course, there is also an element of role-playing to the choice…"
Next week's dev diary is all about Stellaris' multiplayer. After that, you can see a near-complete version (opens in new tab) of the game at the PC Gamer Weekender in March.