This seems to have turned into a more design thread than writing and you seem to have moved on but...

Why not make the setting Stalingrad-ish? A future-human multinational science team have come across an ancient alien hive city of massive scientific importance*. However, in the city they find some sort of nano-forge that would end all poverty blah blah etc etc. However as they are about to test it a group of CIA agents come in to claim it for America. They shoot the scientist (except the yanqui one of course) and take it away. The scientist, seeing the intentions of the agency for world domination, jumps back and uses the Russian detachment's radio to alert Space-USSR.

The two nations quickly polarise back into Nato/Comintern mindsets and war is declared over the massively important artifact.

+2 years

The nations are at a deadlock over the city because it's stepped nature stops them using traditional heavy armour (the advancements in space tech also means any Space-Chinooks would get shot down to. All fighting is close combat urban sludge and casualties are massive. The SUN (space-UN, seeing a pattern here?) is powerless to stop the two superpowers dueling it out. THEN, in a stroke of genius, it is realised that the single surviving scientist knows the city better than anyone else and (because f*** logic) he is a galaxy reknowned tank commander/ fighter pilot AND strategist. They send him in on a special space stealth ship (the UNS Stutter) to spread confusion and dissent. He is given the use of an experimental walking tank to do so (yes, a massive mech is the best way to slip in and out of camps to rabble-rouse). Or the walking tank is leading a taskforce to wedge a buffer between them.

*by hive city I mean the 40k/half-the-sci-fi-out-there artificial mountain which is, importantly, stepped into levels.