The 173rd in Romania, a 1.0 Timeline Option

[Rainbow Six]

I'm not thinking full on internecine warfare so much as one small group, acting as a group within a group. Say you've got a DIA operation going on in Romania and somewhere within that is a three person team. Call it an Orion Team (Orion being the hunter in Greek mythology iirc). They're essentially ultra black ops, boss level opponents. Run into them and it's a serious challenge for a PC group. and if you like to give your players moral dilemmas, there are all sorts of shades of gray in a Milgov / Civgov conflict. And if it's a group within a group, the regular DIA might not even know that they exist.