The universe in question is based on an old scratch-based Sci-Fi/Fantasy/Horror campaign of mine I ran a very long time ago, and was not of sufficent quality to present as-was here. It featured many cliche elements, but it was fun to run. We had battles between cyborgs, demons, Psychotic government agents wiping out anything abnormal, fleet battles, vampires, you name it. Since the PC's were Immortals of highlander fame, you get the picture.
Some of the ideas from that old campaing I thought were still useful, so I have been salvaging what I thought was useful. The background needs work though to make it more generic and less silly. I wanted to present what I had assuming that the ideas were generic enough to meld into other worlds.
But to answer your questions:
In 2450, Humanity is scattered over an assortment of worlds. Some were peacefully colonized, others seized from the alien races that held them. There is no central government, only a shifting set of alliances. One thing that is shared by the worlds are the Rules of Engagement, which serve to limit combat to prevent complete destruction of colonies. Part of these rules include proscriptions against nuclear weapons, along with combative AI's. The second point is a bit gray, as support systems such as the MUL-FS550 Fire Support Robot are close to the line. The fact that a human operator is required to pull the trigger satisfies the letter of the Rules, if not the spirit.
The various planets fight among each other for various reasons - vendettas, trade, resources,etc, but these usually are low-level engagements between professional mercenary groups. Use of planetary military elements is generally considered a dangerous escalation. The Planetary forces are generally used to defend against non-human enemies, where the Rules of Engagement do not apply.
The Robots are built to satisfy various military needs to reduce the imployment of expensive (and perhaps unreliable) mercenary forces, as well as to limit human casulties. Numerous companies manufacture the robots and sell them to pretty much anyone who has the currency to afford them.
I hope this helps! Is anyone interesting in more polishing of this world concept (I know it has elements heavily barrowed from other sources...)