Made of Phlebotinium: Well, while there are several kinds of phlebotinium around (see: Applied Phlebotinium) of one grade or another, the deprivation of most of which would certainly make the universe substantially less pretty and/or efficient, the two big ones from a “made of” point of view would be the Absolutely Ubiquitous Computing, which would have much the same “rocks fall, almost everyone dies” effects were it to suddenly go away as electricity suddenly stopping working in Real Life1, and the specific pieces of ontotechnology responsible for the creation of stargates and tangle channels, without which – and thus with all communications and transport restricted to sub-light speeds – the galactic community would look very different indeed. Indeed, if you delete the tangle channels (which allow real-time communication once you lob them at each other subluminally) as well as the stargates, there’s unlikely to be much of a galactic community, or much in the way of a “star nation” except very loose federations of subluminally-established colonies, bound together by information updates and data trade.
(1. ObVious reference example here: A Fire Upon The Deep, and the Countermeasure.)