Okay, I have an idea for a a PnP RPG inspired by(But not based off of) the Army Men series of games, as well as other sources such as anime, movies, and comic books. I need help in actually developing this idea, with a system, fine details, and an idea for a campaign. These are the factions...

Green Army Men
Tan Army Men
Gray Army Men
Blue Army Men
Cowboys
Natives
Princesses(As in the Sailor Moon anime kind, not the Disney Kind)
Ninjas
Tin Soldiers
Pirates
Samurai
Galactic Alliance
Martians

Hi,

Personnally I think your coming with a very vague idea and would definitely need to sit down just a bit more to think about what you really want for your campaign setting. Because now your talking about cowboys (which were, by the way, not at all in the "same faction" in the real world. Cowboys are much more of lonewolves and quarrel between them was common), about martians, about pirates (renaissance-esque or today Somalia Pirates with guns? And then again, they're far from being in the same faction as each crew strive for economic (and maybe political) power) and about organised armies. The campaign world spans in multiple worlds/galaxies/universes? If not, then where do everyone come from? Why are they so interested in bringing down another faction or being on the world your campaign setting is set. Is there a unique special ressource which everyone from the universe seek?

In my opinion, looking at your tastes (based on your faction list), I'd probably go with one world where there is an actual ressource everyone seeks. It would easily explain the wide variety of soldier-types you have there in your factions, especially the fact that they are from very different ages. well, not so much, but I think you understand.

I hope that helped you a bit in asking yourself the right questions.