In the region of space where your world exists, conquest is not allowed. It is strictly forbidden, and this rule is maintained in order to assure order and stability within this neighborhood of life. If one race seeks to gain advantage in another inhabited world, it must do so in such a way that it appears that its presence is welcome in that world and that a mutual agreement has been established.
This is very important to understand in your world, where intervening forces are already here attempting to establish influence. Should it appear to outside observers that their presence is at least tolerated, if not welcomed, then there will be no effort on the part of other nations to restrain their presence here.
But should humanity exercise its authority and proclaim that it does not seek intervention and does not welcome those races who are present in the world today, then those forces must withdraw or face considerable difficulties from their competitors and from other nations in the region.
While others in your neighborhood of space are not free to dominate your world through conquest and through military force, they are entirely free to gain influence here under certain conditions. And they would not hesitate to want a world such as yours as part of their network, as one of their primary clients or as a resource within their sphere of influence.
It is not yet certain whether humanity can sustain this kind of wisdom and restraint. Even now you have very little else to conquer in your own world. You have your solar system to explore, but you will find very few places where you can make any establishments at all, and even these will be difficult to maintain. You will have to face and are facing even now the pressure of influence and persuasion created by opportunistic groups in your region of space who are here to do business, who want to extend their power and influence through means that are within the bounds of what is tolerated.
