Below is the complete list of all countries, categorized under a specific tech group.
Formable nations are countries, normally cultural unions, that don't exist in 1444 but can be created by any nation if the specific requirements are met.
Major powers are nations that have: some sort of specific flavor events, has unique ideas and are a regional power
A country is classified as a regional power when their overall performance excels those of their lesser neighbors. This can be measured via one's military strength, naval power and if an economy is strong.
Minor powers are the rest who do not qualify as being 'strong' nations.
1 Means that the nation does not exist at the 1444 start. Formable countries are not included. 2 Means that the nation can only exists if converted from Crusader Kings II.