Perhaps, the "Sioux aliens" aren't native to the system at all.
They're from a nearby star system, this is one of the first star systems they've reached after developing warp drive. Their sole claim to the entire system amounts to "we were here first," and also "our home system is closer that yours."
... a vast asteroid-field ...
Our own asteroid belt (the inner one) has a circumference of over a billion kilometres.
who object to this sudden influx of aliens into their territory
The Sioux aliens have claimed the belt in it entirety, they are thinly spread through the belt, and only inhabit a small portion of it. They lack the technology to enforce their claim, and have resorted to isolated raids to encourage other to leave. Sometimes it works.
One story might follow two young men arriving in what is essentially an oversized shuttlecraft
Another story might follow a larger, more well-funded mining ship and its crew.
The belt is slowly in the process of being divide up. Different species, not all from the Federation are arriving. Some are new comers, other have been there for decades, individual miners and also a few professional mining companies (Ezra Dax's family-like). And a couple large corporations too, causing friction with the independents.
Small sections of the belt are "de facto" the property of this or that species.
I wouldn't place it in the Picard-era 24th century, somehow I can't see hundreds of thousands of people having any sort of motivation to leave the safety of Federation space to seek their fortune in the unknown.
Not everyone wants to be taken care of and be provided for. You'll alway have a segment who want to build their own lifes, with their own hands.
No one mentions telling the tale from the viewpoint of the "Sioux" aliens ...
That would be one story possibility, are they of one mind concerning the raids? Some of them might just be traders, settlers, miners. Each with their own story.
This whole thing might work best as a anthology.
Starfleet ... hamstring them so they weren't massively involved ... but is unable to legally stop Federation citizens from going out there.
If the Federation (or Starfleet) are in over all control, this becomes far less interesting, we lose the "wild west" aspect.
I would think that an Archer-Class ship (the 50m long scout from Vanguard)
And maybe a number of runabout size ships, and sublight shuttles as well, operating off of a beat up old carrier, vintage Romulan War era, it basically loses it warp drive after it arrives.
But then again, I love small ships.
Me too. You send in a "flying starbase' type ship and it wreaks the premise.
The Prime Directive exists in the TOS and TNG eras ...
But the Prime Directive in TOS, and the Prime Directive in TNG are so different, it's basically two different "laws" with the same name.
interfering with the Sioux aliens is a violation of it because they exist outside of Federation space.
The Federation might not recognize the Sioux alien annexation of the entire system. Starfleet did go to the defense of the settlers who moved into disputed space, protected them from the Cardassians.
No special treaty is required to keep Starfleet from helping. All Starfleet and the Federation have to do is obey their own law.
But which law, during which time period? Even if Starfleet's presence wasn't to fight the aliens as a group, they could still protect the settlements from attacks. Problem would be the mines and settlement are scattered, and Starfleet is thin spread.
Starfleet might also be there to prevent the settlers from attacking the aliens in response. Plus there are other aliens besides the Sioux.
In fact, in this situation their likely course of action would be to forcibly remove the settlers to Federation space, ending the prospecting and the story.
The settlers are from planets within the Federation, who want their species/people protected, their families who remained behind would call for it, and their representatives in the Federation Council would listen. There might be elements in the Council who see this rich system and want the Federation to one day swallow it.
your man on the street Federation citizen is not bound by the Starfleet MO and can do as they please.
Especially if they are outside the Federation proper.
then Starfleet would likely respect their wishes and not infringe on their territory again
Again, if Starfleet recognized their claim that the asteroid belt was entirely their territory.
because having contact with a race that wants no contact can be considered "interference with their natural development."
And Starfleet can say, "fine, we won't interfere with you and your settlements, and you don't interfere with ours ... we clear?" Plus there nothing that says that there is any contact with the Homeworld of the Sioux aliens at all. Just those of the Sioux that ventured to the asteroid belt.
Due to the Prime Directive, I believe Starfleet would only have made first contact with the Sioux-Aliens if they were warp capable.
If Starfleet got to them prior to the private interest getting there first, Starfleet might be coming in late in the game, after much of the situation was already in place.
The miners, settlers, traders, transporters and such were up and running, when Starfleet first entered the system.
What you're all missing is that this concept doesn't work if Starfleet or the Federation is involved at all.
No, it would depend on the level of involvement. If we're discussing "only" tens (or hundreds) of thousands of people out of the Federation, how much in the way of assets is the Federation really going to throw at the problem?
It's perfect if it's prospectors going out into the great unknown and meeting natives nobody knows about and get in trouble with them
If that happens first, yes. And I agree that Starfleet should not be the main focus of the story (or stories).
To be honest I can't see Starfleet not noticing or finding out that thousands of Federation citizens have all upped-sticks and left for parts unknown.
A hundred thousand people (if that), out of a trillion? That would be like 32 people disappearing out of the American population.
I like the idea of being set in the mid-23rd century
Look at the miners in Mudd's Women. Something like that.
Starfleet ... It would work better if they were always in the background,
Yes, minimal presence.
