[quote=WrongEndoftheRainbow]
Looking into it more, it seems it's called inter-dimensional teleportation, but what it does is figuratively 'tunnel' to different universes. Imagine a jar of fruit, the inter-dimensional teleportation would let one of those pieces of fruit teleport to another jar of fruit in an entirely different household, but not anywhere in the original jar of fruit. I'm guessing the dimensional/universal teleportation error is gamedev made.
[/quote]

[quote=darkwolf687]
Its multi-universal empire. They are known as the universal union and they control an unknown but likely large number of universes by using their advanced dark energy teleportation devices to zip into different universes and grab them for their empire. Also, we don't know what invaded Earth. Its implied by Breen, (especially if you consider its function to serve as a link, a bit like constructing a dock) and a line from hl2 raising the bar that the citadel appeared after the surrender (The war lasted seven hours, the citadel, according to raising the bar, replaced entire blocks of the city overnight, which thus might be after the seven hour war) The majority of the invasion force has already left too, what we see in hl2 is just an occupation force, and its possible they used other types of more deadly synths (we see some in the game we never fight, and the hunters didnt turn up till white forest making it possible that the combine had reserves of forces that we know nothing about) hence why they try to call for reinforcements and Vance comments the Resistance wouldn't last seven minutes.
[/quote]

We're probably definitely going to see what QueenRaidne says. The fact that they are Inter-Unviersal might mean it would be a good idea to think of something else(This is being based upon what I know about Raidne and the RP.) for one, Assallyas Kiith probably would insta target Combine. Which would be interesting to watch actually. Secondly, if you are inter universal that means the Combine can send you reinforcements whenever they want as soon as they find out where you are. Which kind of defeats the purpose of having to band together with other players :P