A great power is a sovereign state that is recognized as having the ability to exert its influence on a global scale. There are eight of them at any one time. Being a great power opens up several opportunities, as well as responsibilities - participating in crises the most notable. Great Powers can, in the late stages of the game, cause a Great War.
Secondary powers are not as powerful as great powers, but will usually be capable of standing on their own. They are able to colonise, although may face heavy competition from great powers. There are eight secondary powers.
All great and secondary power count as civilized, but here this refers to the particular class. Civilized nations are westernised. They are unlikely to be able to defend against an aggressor nation, so will require outside assistance. There is no limit to the number of civilized nations, and they cannot be demoted (although they can be promoted to secondary power).
Uncivilized nations are not westernised. They are burdened with numerous disadvantages which will affect their growth, and can easily be defeated by a greater nation. There are three categories of uncivilized nation. depending on their level of civilization:
- Primitive nation - Below 15%
- Uncivilized nation - 15% - 50%
- Partially westernized nation - 51% - 99%
Those categories have no effect on the nation, besides the effects of the reforms it has made. It is purely flavor.