The real question is why is Scotland separate from England here? I think it would have been better to just branch off the British Empire as simply the Commonwealth and add space for other nations to go in.
I think it's more of an "Axis v Allies" kinda thing rather than "Nation v Nation" thing. Since all the unit decks are represented by divisions (like the US 101st) and since the UK had Scottish Divisions, it's likely that is how Scotland is being represented.
In other words: In Wargame we had BLUFOR v REDFOR, with the US/UK/GER/FRA/et al. on BLUFOR and USSR/CHINA/POLAND/et al. on REDFOR. In Steel Division we'll have the 101st US Airborne (and others) on ALLIES and the GER 12th SS (and others) on AXIS.