If you don't have steam, you must not have Sins of a Solar Empire Rebellion. You may have one of the earlier versions of Sins, such as trinity. If you tell us exactly what version of Sins you have we might be able to forward you to one of the Star Wars mods for that version.

Okay, that makes a lot more sense.   Can you tell us your exact version number (it is displayed in the lower right hand corner from the main menu), so we can tell you if you need to update or not.

I don't think SoGE has a Diplomacy version, but Star Wars Requiem does if you don't mind not having the Clone Wars era. Otherwise with Trinity you can manually use the "Entrenchment" expansion only to play an older version of SoGE.