I want to make neutral planets for a 4X space game. I mean like some unique race that live on that planet only (not expanding ever) and providing some services, or selling unique stuff no one else can produce or a trading center planet.

I look how to fit it into 4X mechanics (which is basicly a planetary conquest). How to make it so the player does not want to conquer these (easier)? And what happens when an AI race conquers it (some of these AI races are just stupid bugs that don't care, they will conquer it on sight) (harder)?

I'm especially concerned with the AI races (so to avoid a situation where all these unique one planets societies extinct before the player has the chance to even meet them...)

Make them a hard nut to crack (to require significant resources to 'take', compared to the gains of controlling it..)

Alternative to that is having it be MORE beneficial to trade/interact, with them remaining Neutral (and to deny that benefit to your enemies).

They then have to be pre-built up sufficiently with whatever production/facilities/populations your game mechanics support OR generalized/Abstracted in a seperate mechanic

How well a 'ally' cooperates and what options you have to 'handle' them is an added complexity to the game.

It might be possible that these neutrals be more than one planet/system (even if just a variant with 2 right next to each other to vary the situations)

The politicing/negotiation systems if too complex might start moving off the style of the game if they get too complex. So some simpler random 'reaction table' to set their stance towards you and they then become 'part of the terrain' where you can agressively explore to find the 'good' ones and then leave the bad ones to be 'handled' later (or an important immeiate goal if its at some chokepoint tothe players expansion...)

Similar to wodinoneeye said.

In real life neutral countries exist because either:

1. The conflict hasn't expanded yet enough to affect them.
2. They're strong enough to repel any invasion if they get involved (they could even seriously imbalance the war if they take side).
3. Most of the involved parties don't want anything of that country (i.e. why would Israel or Palestine want to take umm... Mexico?) or are emotionally attached to them (emotion != logic).
4. It's more beneficial to have them as an independent country than to have them take your orders. May be because their know how is too high and can't be used appropiately if you invade them, or their citizens could start small acts of terrors during the occupation, or guerrilla style fighting.

For a game, points 2 and 4 are the most interesting. Point 4 can actually be very fun and make the player go through a living hell.

Point 2 is easy. If you attack, you will be obliterated.

Point 4 is fun. You can attack, you may win. But pay the consequences until you release that land back. Random sabotages, slowdown of your resources gathering or slower building of units, critical unit-making buildings randomly exploding, inability to develop certain technologies. Allow the development of technologies or gathering the goods they offered when they were neutral, but at a higher price (or getting developed at a slower rate), etc.

Point 3 is possible if the game has a story. Get the player to actually love a civilization good enough so that most players will feel bad about invading it and prefer working alongside them. But this is really hard to execute well.

If they can make something out of resources that would otherwise be unnecessary to you, then they are better kept alive.

Example:

A species of big worms that have absolutely no organization, etc, but they can slowly turn dirt into gold (or whatever) because that is what their digestive system does.

Now, if you bring them this otherwise mundane dirt, they start having value. Conquering their homeworld will never be nearly as interesting as piling up dirt on their world and reaping the rewards.

It just needs to be a species or culture that values freedom more than life, and is generally pacifist otherwise.

If you try to take them, they could just self destruct or something.

Add to that, as you said, that they do or produce something very useful, maybe you are only driven to control the space around them and prevent the enemies from accessing the planet so you get exclusive trade with them (which is almost the same as taking the planet).

Or did you want to avoid that too, so that they really do trade with every faction no matter what?

As for your AI, you can easily program them to not take the planet; just have them do a check when deciding to take a planet, and make it always a 'no' when it's this type of planet.

Along the lines of the other posters responses, you might try some sort of species which is both technologically and societally advanced far beyond the player and AI species. They've developed their society to the point that they have no need for expansion (perfect population control, etc), and while their advanced technology makes trade with them advantageous, it also allows them to swat down (hard) any species which try to invade them.

Along the lines of the other posters responses, you might try some sort of species which is both technologically and societally advanced far beyond the player and AI species. They've developed their society to the point that they have no need for expansion (perfect population control, etc), and while their advanced technology makes trade with them advantageous, it also allows them to swat down (hard) any species which try to invade them.

Yes, but why would such an advanced species bother trading with these warring barbarians? What would they have to gain?

And if they did it for our benefit... aren't they just fueling our war machines? If they have conscientiously and ethically advanced, wouldn't they refuse to trade with us at all until we grew up and started getting along with each other?

To that end, maybe they would have stipulations for trade.

Like:

"If you really must fight with each other, then fine, we can't stop you and you have to learn to get along with each other by yourselves in your own time. But, we won't trade with you if you attack civilian targets. We'll know. We're watching. And we won't give you weapons, only medical technology to treat your injured and sick, and shields to protect yourselves against attack."

I just remembered from KoToR that planet Manaan was a neutral zone providing "kolto" which has amazing healing power so neither of parties would dare to invade there as they threaten to destroy source of kolto in that case.

One possible reaction to an invasion of a neutral planet could be that all the other races unite against you.

Neutral planets could create buffer zones between empires that would have to be annexed prior to an invasion and also act as way defending yourself from an enemy.

Neutral planets might have key exports and imports making them significantly more valuable as trading partners then they would be to conquer.

Neutral planets might encompassing many unique bonsues things for instance a research colony might provide a free technology once you've supplied them with a set amount of trade goods.

Neutral planets could be used to fight proxy wars. Why attack your enemy when you can get a neutral race to do it.

Rare planets could be sold to private individuals and corporations for massive one off bonuses becoming neutral worlds.