Is there some way to keep other factions out of my systems without declaring war?

[Psycho 78]

Title says it all, I want to protect my assets without having to shoot on sight.

[Silamon]

As far as I am aware... nope. Borders don't exist.

Diplomacy in this game is extremely basic.

[Gregorovitch]

In DW1 you could threaten an empire that built a mine or something in your territory via diplo. You could also negotiate station swaps when borders shifted. I can't say if you can do that in DW2 or not.

If a faction sends military ships into another's territory then that damages their rep. Cumulatively. That does not apply to civilian ships like traders and explorers. All factions are free to explore and trade wherever.

You are free to shoot up another empire's military ships violating your space without penalty, it is not considered an act of war/aggression in of itself. Although the very presence of such ships may be an indication the empire in question has hostile intentions.

In practice if you do shoot them up they will probably just jump out of the system. Sometimes they were just there 'cos they were exploring or trying to chase something or looking for a pirate base. In other words they didn't know you were there and they'll leave you be for now. Other times, well, they did and most likely they will be back. Mob handed.

Which is to say if you don't want to cozy up to 'em you might as well shoot 'em up and chase them away. What they do about that subsequently will tell you a lot a bout their intentions.

[Ornlu Wolfjarl]

Originally posted by Psycho 78:

Title says it all, I want to protect my assets without having to shoot on sight.

If your influence (colour) covers the system, then no other empire can build anything there, unless they have a treaty with you (mining rights for mining stations, migration treaty for colonies (not sure if it actually works, but this treaty seems to re-enable the buttons on the new colonies screen for colonizing planets), research treaty for research stations.

If a foreign empire has already build stations before you gained control of the system, then those stations remain theirs. However, you can negotiate their ownership by "Negotiate a deal" in the diplomacy screen with that faction. Each such station costs about 40-50 thousand credits worth, so it's not hard to acquire them, if you have at least neutral relations with the other empire.

As Gregorovitch said, you can shoot up any military ship that enters your territory without a declaration of war. Doing so, does damage relations though.

If you see increased foreign activity in one of your systems, particularly military presence, then it's best if you station a fleet to the system and be ready for hostilities.

[Dray Prescot]

If someone has a Mining Station at a World, and someone else builds a Colony at that World, The Mining Station disappears.

I am not sure about Research Stations and Resort Bases. I do know that they can be built in orbit of IND Worlds. Since I usually was the one who eventually colonized those IND Worlds, I am not completely certain about ownership if someone else colonizes that IND World. I think, maybe based on one or two cases months ago that I may not remember correctly, that I kept control of a Research Station or a Resort Base if that happened. (But I may be wrong).