I've seen a fair majority of the material which comprises primary Star Trek canon. I've watched all the TNG-era shows, all the movies (as far back as The Motion Picture), and am currently working through the Enterprise series.
Through all this time, I've seen Starfleet make First Contact with a wide variety of species in many different stages of development. However, there's one particularly interesting scenario which I can't recall ever having seen happen. It's possible this will happen in an episode I haven't seen yet (i.e.: Enterprise Season 2 or later, or any TOS/TAS episode) or I may have just forgotten it.
What I'm looking for is a situation where Starfleet has made First Contact with a race that meets both of the following criteria:
- Already has and has been using warp technology for quite some time - not just recently developed.
- Is, until encountering Starfleet personnel, oblivious to the existence of intelligent alien life forms.
Has this happened in Star Trek history? If so, which episode?
As Seven scans the surface she detects warp experimentation. Soon after, Voyager is being attacked by antimatter torpedoes and a tricobalt device.And it's hard to define "quite some time" given the timey-wimey in this episode. Anyway it's the best fit I could think of.