I feel like the most obvious contenders are Iran and Vietnam. Libya, Chile, and perhaps a broad topic like the Cold War specifically honing in on the US and the Soviets could be really interesting.
Also given that they teased Ukraine at the end of s4 a Soviet season could tie in nicely to ease into talking about Ukraine for season 6 although that really depends on how things play out given the war is still going on and who knows where we’ll be going into 2025. (S5 is totally out of the question for talking about the current war imo) a broad topic like that could prove a challenge fitting it into ten episodes they may have to do some hour and a half episodes for this one as not to feel rushed.
Vietnam would be fun because I feel like all the ho-chi-Minh action would be sick as hell. Lots of intrigue and overlap with what was happening in Vietnam with what was happening with the wider left in the US would be dope as hell.
Iran would be extremely good. The buildup to the fall of the shah could be a whole season in of it’s self without even getting to the contemporary era plus lots of leftist intrigue going on in that period.
Curveball guess? Maybe something covering the Balkans/Caucasus depending on the conflict in Armenia turns out and maybe dabbling down into Greece and Italy, get some Gladio in there if things get a little sparse.
Balkans would be interesting. Some Mujahideen fighters were actually sent there by the US to stir up trouble, but they were stabbed in the back and forced to either return to their countries of origin or be arrested. I've heard (though unfortunately, I can't for the life of me think where) that this was one of the real reasons for 9/11 - Bin Laden was pissed off that the CIA fucked him and his friends over.
Idk about you but that sounds like it'd be part of the show...
besides that, the Yugoslav wars would be interesting as a small part of the show, perhaps like "Red-Handed Sleight of Hand" where they focus on Socdem Guatemala's coup d'etat, in context of Revolutionary Cuba's actions...
lol
(curveball was the pseudonym of one of the iraq WMDs sources mentioned in blowback)