I spent some time simplifying that map I found to make it more fitting for a board game without dumbing it down too much. Fairly satisfied with the division of the US (even if some regions could be combined), but Europe is tough. Here's a brief outline of what I have so far. The production values in parenthesis (for reference, a basic infantry unit costs 1) are flexible but the new regions themselves will be difficult to cut up again. It's doable but combining them is easier (and will have to be done)
United States has 19 regions: Washington (1), New England (2), New York (4), Atlantic (3), Upper South (2), Virginias (2), Carolinas 2, Deep South (2), Louisiana (2), Texas (3), Steel Belt (3), Great Lakes (3), Midwest (2), Great Plains (2), Dakotas (1), Southwest (1), Rockies (2), Cascadia (2), California (3)
The Union of Britain is composed of 4 regions: London (5), Manchester (4), Wales (1) and Scotland (2)
Ireland has Dublin (2) and Ulster (1)
The Commune of France has 8: Paris (3), Normandy (1), Brittany (1), Aquitaine (2), Occitainie (1), Marseilles (2), Auvergne (1), Grand Est (1).
Austria+Illyria has 8: Vienna (2), Tyrol (1), Trent (1), Styria 1, Trieste 2, Croatia (2), Bosnia 1, Montengro 1
Red Italy has 3: Piedmont (2), Tuscany (2), Emilia (1)
Republican Italy has 2: Milan (2), Venice (2)
Monarchist Italy (with Papal states) has 5: Rome 2, Naples 2, Calabria 1, Sicily 1, Sardinia 1. Thinking to enlarge Rome a bit and have Naples combined with Calabria
Serbia is 1 region worth 2
Spain has 5: Madrid (2), Castille-Leon (2), Andalusia (1), Catalonia (2), Basque country (1)+Spanish Morocco (1) and Sahara (maybe)
Portugal has 2: Lisbon (2) and Norte (1). Colonies will be 2 or 3 provinces.
Haven't touched Switzerland but it'll be reduce to 1 or 2 provinces at most.
Flanders-Wallonia are Flanders and Wallonia, both worth 2 (and without German annexation they're already a puppet and the map looks nicer this way)
Bulgaria will be 3 provinces.
Romania 2 or 3
German and Austria puppets in the East will be reduced to 1 province, except for Ukraine.
Scandinavian countries and Finland will each have 2 provinces (3 for Denmark but Greenland will give nothing except real estate)
Greece will be at least 2 (mainland+Crete)
Mexico will be in 5 or so. Central and South America in general seems easy to do
Germany isn't done at all (besides Alsace-Lorraine and the Rhineland. It should have around 9. Hungary should have Slovakia (already done)+3 or so others. Bohemia should be 2.
Ottoman Empire will be hellish. So will Russia, Africa and Asia.
Anyway, here's the less tedious part. The game will need at least 3 players (Entente, Reichspacht and Internationale), but will have potentially many more. There will be two theaters that can be played standalone or combined in a global game: Europe/Africa and Asia/America. Other main factions are Russia, the Ottomans and Austria-Hungary for Europe/Africa and the US and Japan for Asia/America. The start of the game (1935) will look like this:
Europe/Africa
Entente: National France, Portugal, Monarchist Italy, South Africa
Internationale: Commune, Union of Britain, Socialist Italy
Reichspacht: Germany and puppets (Belgium, Ukraine, Ruthenia, Poland, you know the drill), Mittelafrika
Other playable factions: Russia, Ottomans, Austria-Hungary
Asia/Americas
Entente: Canada, West Indies, ANZAC, part of India
Internationale: Mexico, Chile, other part of India
Reichspacht: Qing China, German legation cities
Other playable factions: US, Japan
The goal for a 3 player game is for your faction to directly defeat the enemy or get enough neutral countries on your side. How do you do that?
First, you have 2 resources: production given by your provinces, and political support that you can get through having independent countries on your side or by using policy cards that all have different costs (for example, passing improved welfare laws in Germany can get you 1 per turn after spending X production for it, going full Totalist in Britain could give you 5 as a one time deal and locks you from other policies). You can use your resources to buy an army to crush the filthy reds/liberals/populists/monarchists directly, or to get policy cards that give you a foothold there. Let's say Germany wants to get involved in South America to counter the syndicalists. You can buy the policy card that makes Argentina join the pact to counter Chile, which would be easier if the syndicalists invaded it. On the other hand, if Chile didn't invade Argentina, their policy to support Patagonia would be cheaper too etc.
How do the major neutral powers work? If non-playable, they'll be able to be influenced in similar ways to other neutrals: get the Bolsheviks to rebel as the Internationale, make Austria join the Central powers again, get Japan to fight Qing and Germans for the Entente etc. If the power is actually played by a person, things will be interesting. Let's take the US as an example. They'll be able to get select of four parties to win the Presidency: it's Socialists, Longists, moderate republican/democrat (may be 2 candidates) or the far right (think KKK, extreme Dixiecrats etc.). Each party can align with one (or two) of the main factions or chose to stay on its own. If say, the Reichspact opposes the Reed Presidency (who may stay isolationist or join the Internationale), they can back the nationalists or the Longists, getting a small army in the US. Of course, the US player will be now very interested in joining the Internationale, but maybe their first strategy didn't need this alliance and you created your own enemy.
Alternatively, you can pick and choose the countries/factions to use if you have enough players. One Internationale player plays the union of Britain and Chile, the others plays Mexico and France; everyone plays a different side in the 2nd ACW etc. This is still at a very rough stage. It's way too complex and needs to be playtested.
EDIT: here's the map so far
United States has 19 regions: Washington (1), New England (2), New York (4), Atlantic (3), Upper South (2), Virginias (2), Carolinas 2, Deep South (2), Louisiana (2), Texas (3), Steel Belt (3), Great Lakes (3), Midwest (2), Great Plains (2), Dakotas (1), Southwest (1), Rockies (2), Cascadia (2), California (3)
The Union of Britain is composed of 4 regions: London (5), Manchester (4), Wales (1) and Scotland (2)
Ireland has Dublin (2) and Ulster (1)
The Commune of France has 8: Paris (3), Normandy (1), Brittany (1), Aquitaine (2), Occitainie (1), Marseilles (2), Auvergne (1), Grand Est (1).
Austria+Illyria has 8: Vienna (2), Tyrol (1), Trent (1), Styria 1, Trieste 2, Croatia (2), Bosnia 1, Montengro 1
Red Italy has 3: Piedmont (2), Tuscany (2), Emilia (1)
Republican Italy has 2: Milan (2), Venice (2)
Monarchist Italy (with Papal states) has 5: Rome 2, Naples 2, Calabria 1, Sicily 1, Sardinia 1. Thinking to enlarge Rome a bit and have Naples combined with Calabria
Serbia is 1 region worth 2
Spain has 5: Madrid (2), Castille-Leon (2), Andalusia (1), Catalonia (2), Basque country (1)+Spanish Morocco (1) and Sahara (maybe)
Portugal has 2: Lisbon (2) and Norte (1). Colonies will be 2 or 3 provinces.
Haven't touched Switzerland but it'll be reduce to 1 or 2 provinces at most.
Flanders-Wallonia are Flanders and Wallonia, both worth 2 (and without German annexation they're already a puppet and the map looks nicer this way)
Bulgaria will be 3 provinces.
Romania 2 or 3
German and Austria puppets in the East will be reduced to 1 province, except for Ukraine.
Scandinavian countries and Finland will each have 2 provinces (3 for Denmark but Greenland will give nothing except real estate)
Greece will be at least 2 (mainland+Crete)
Mexico will be in 5 or so. Central and South America in general seems easy to do
Germany isn't done at all (besides Alsace-Lorraine and the Rhineland. It should have around 9. Hungary should have Slovakia (already done)+3 or so others. Bohemia should be 2.
Ottoman Empire will be hellish. So will Russia, Africa and Asia.
Anyway, here's the less tedious part. The game will need at least 3 players (Entente, Reichspacht and Internationale), but will have potentially many more. There will be two theaters that can be played standalone or combined in a global game: Europe/Africa and Asia/America. Other main factions are Russia, the Ottomans and Austria-Hungary for Europe/Africa and the US and Japan for Asia/America. The start of the game (1935) will look like this:
Europe/Africa
Entente: National France, Portugal, Monarchist Italy, South Africa
Internationale: Commune, Union of Britain, Socialist Italy
Reichspacht: Germany and puppets (Belgium, Ukraine, Ruthenia, Poland, you know the drill), Mittelafrika
Other playable factions: Russia, Ottomans, Austria-Hungary
Asia/Americas
Entente: Canada, West Indies, ANZAC, part of India
Internationale: Mexico, Chile, other part of India
Reichspacht: Qing China, German legation cities
Other playable factions: US, Japan
The goal for a 3 player game is for your faction to directly defeat the enemy or get enough neutral countries on your side. How do you do that?
First, you have 2 resources: production given by your provinces, and political support that you can get through having independent countries on your side or by using policy cards that all have different costs (for example, passing improved welfare laws in Germany can get you 1 per turn after spending X production for it, going full Totalist in Britain could give you 5 as a one time deal and locks you from other policies). You can use your resources to buy an army to crush the filthy reds/liberals/populists/monarchists directly, or to get policy cards that give you a foothold there. Let's say Germany wants to get involved in South America to counter the syndicalists. You can buy the policy card that makes Argentina join the pact to counter Chile, which would be easier if the syndicalists invaded it. On the other hand, if Chile didn't invade Argentina, their policy to support Patagonia would be cheaper too etc.
How do the major neutral powers work? If non-playable, they'll be able to be influenced in similar ways to other neutrals: get the Bolsheviks to rebel as the Internationale, make Austria join the Central powers again, get Japan to fight Qing and Germans for the Entente etc. If the power is actually played by a person, things will be interesting. Let's take the US as an example. They'll be able to get select of four parties to win the Presidency: it's Socialists, Longists, moderate republican/democrat (may be 2 candidates) or the far right (think KKK, extreme Dixiecrats etc.). Each party can align with one (or two) of the main factions or chose to stay on its own. If say, the Reichspact opposes the Reed Presidency (who may stay isolationist or join the Internationale), they can back the nationalists or the Longists, getting a small army in the US. Of course, the US player will be now very interested in joining the Internationale, but maybe their first strategy didn't need this alliance and you created your own enemy.
Alternatively, you can pick and choose the countries/factions to use if you have enough players. One Internationale player plays the union of Britain and Chile, the others plays Mexico and France; everyone plays a different side in the 2nd ACW etc. This is still at a very rough stage. It's way too complex and needs to be playtested.
EDIT: here's the map so far