Some Neutrals stats supplied by Ryan Hanson on BGG:
Central Powers Aligned
Bulgaria
Aligned to: Ottoman Empire
IPC Value: 3
Historical Population: 4,800,000
Historical GDP: 7.4
Historical 1914 Standing Army/Reserves: 280,000
Historical Total Troops Mobilized: 1,200,000
Allied Powers Aligned
Serbia/Montenegro
Aligned to: Russia
IPC Value: 2
Historical Population: 7,000,000
Historical GDP: 7.2
Historical 1914 Standing Army/Reserves: 250,000
Historical Total Troops Mobilized: 757,000
Romania
Aligned to: Russia
IPC Value: 2
Historical Population: 7,700,000
Historical GDP: 11.7
Historical 1914 Standing Army/Reserves: 290,000
Historical Total Troops Mobilized: 750,000
Belgium
Aligned to: France
IPC Value: 2
Historical Population: 7,600,000
Historical GDP: 32.4
Historical 1914 Standing Army/Reserves: 117,000
Historical Total Troops Mobilized: 267,000 (seems too low?)
Portugal
Aligned to: France
IPC Value: 2
Historical Population: 6,000,000
Historical GDP: 7.4
Historical 1914 Standing Army/Reserves: 40,000
Historical Total Troops Mobilized: 100,000
Albania
Aligned to: Italy
IPC Value: 2
Historical Population: (?)
Historical GDP: (?)
Historical 1914 Standing Army/Reserves: (?)
Historical Total Troops Mobilized: (?)
Note: Larry has reported that Albania also includes Montenegro and is really more of an amalgamation of that region than a specific nation state. It exists primarily for game purposes.
Arabia
Aligned to: British Empire
IPC Value: 1
Historical Total Troops Mobilized: (?)
True Neutrals
Netherlands
IPC Value: 2
Historical Population: 6,210,000
Historical GDP: 22.0
Norway
IPC Value: 4
Historical Population: 2,450,000
Historical GDP: 6.0
Sweden
IPC Value: 4
Historical Population: 5,620,000
Historical GDP: 15.8
Denmark
IPC Value: 2
Historical Population: 2,830,000
Historical GDP: 10.6
Spain
IPC Value: 4
Historical Population: 20,200,000
Historical GDP: 41.6
Switzerland
IPC Value: 1
Historical Population: 3,860,000
Historical GDP: 16.5
Greece
IPC Value: 2
Historical Population: 2,730,000
Historical GDP: 4.0
Persia?
Afghanistan?
Ethiopia?
If anyone has any of the missing numbers I would appreciate it.