I don’t believe there will be a historical assessment to teurality in the game - it will just add flavor…
Spain: Franco was a clever politican -he used Germany and Italy in the SCW, but refused to take an active part in the war (allowing the Blue legion is not something considered active participation - I belive therwe were French, Dutch Belgian, Norwegian volunteers fighting for Germany/against communism). - Ingame I think Spain will be a true nutral, because it never delared war on Germany.
Same for Sweden and Switzerland
Turkey might be true neutral too, but maybe it will have some triggers to join in if Russia get bashed…
I think true neutrals might never declare war, but can be attacked by either side (attack on a neutra could cause pro-xy neutrals joining the cause of one side or another)
for example Bulgaria : pro Axis, if Germany attacks Greece then Bulgaria will become Axis…
Romania (Hungary) pro axis - will join when Germany attacks Russia
Romania, Hungary and Bulgaria are the classics ;)
Portugal sided early with the Allies IIRC
Iraq/Iran might (should) be pro Axis, but may not become active easily and an attack ON them should be possible without penalties for the Allies
Ireland - maybe true neutral (depending on mapsize Irland could be a nice staging point for the Luftwaffe ;)
Yugoslavia might be pro Allies - can’t think of a trigger atm
South America (if its part of the game, I think the only pro Axis countries could be Argentine (rivalry with Brazil -which should be pro Allies…) an Paraguay/Uruguay. - others could be True NEutrals but easily swayed to the Allies side…