ST TNG's first contact, the episode not the film.
We finally get to see what the Federation looks like from the perspective of a new species making it's first timid steps out into the greater galaxy.
Oh boy is it terrifying, not the least is the fact that their homeworld is within deep Federation space
They have agents on their homeworld that look and act enough to pass as Malcorians and technology to teleport anywhere on their world. The appearance of a galaxy class starship for a culture complerely unfamiliar would probably look like the scene in SG1 where Anubis' ship appears right above a Kelownan city.
But even as Riker was captured by the already xenophobic malcorians, Picard's diplomatic acumen managed to save the relationship. By providing the Malcorians total control over the diplomatic process, aside from the initial "first" contact and by indicating the Federation will respect Malcorian wishes first and foremost, even as they are in a position of total power, it shows the Malcorian leader that though they should pursue relations, they aren't ready.
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The Genii from Stargate Atlantis.
Here is a culture that managed to conceal itself from not just the Wraith but from the entire galaxy as a survival strategy.
And then...here shows up a brand new human culture with more advanced weapons and other advanced technology (radio by Pegasus standards is incredibly rare, and radios the size of what Earth has, basically non-existent) and then proceeds to demonstrate that they could detect who the genii really are underground. Ontop of that McKay deduces from an interrogation cell that the key to their whole plan is an atomic bomb. And then Sheppard reveals that they not only have the ancient gene but also access to Lantean technology.
Yeah, they were never going to react well. This fear as well as Earth's overconfidence sets the tone for their entire relationship to follow. Human enemy civilizations in Stargate didn't really exist as an arc aside from the Genii.
Teyla joining with Earth immediately set off alarm bells in the minds of the genii. They knew that Earth had to have something big for Teyla, like themselves will do anything for their people. She wore an Atlantean uniform, made of materials unknown to the genii, carrying a weapon beyond their technology. It looks like her people were conquered and she is happy about it.
Then there is Sheppard who was a friendly face. But this is the Pegasus galaxy, where if the Wraith don't feed on you, other humans will kill you for your trinkets. The galaxy is dark and full of terrors. Smiling while meeting a new people would mean you're hiding a knife behind it. Indeed when Sheppard lied about their invisible ships ...and proving they had if not access to but the ability to make nukes, basically meant they were doomed to be enemies.
As a resource based culture they also maintained indirect control of a large number of planets as a sort of vassal empire causing huge problems for Atlantis which had no trade footprint other than information, some diplomatic relations and food.
But yeah, fascinating culture the genii and a group I wish the writers did more with.