The rank of your nation determines how big of a country you currently have. This way, you can also determine how strong is your enemy, as more cities means more taxes, gold, manpower, as well as strong army and fleet.
The only way of increasing your rank is getting new cities under your control. You can sell cities to nearby nations, but not all of them will want your land. The cities of subject nations are not counted towards to the amount of your cities, needed for leveling up. Every rank offers different bonuses and new options that affect your playstyle.
Imperator: Rome offers following country ranks:
- Migrant Horde and City State. This is the smallest type of nation that can exist in the world of the game. They offer special bonuses, for example, a Horde can migrate without having a single city, while City States offer a bonus to fort defense.
Organized tribes, kingdoms, and republics are divided into:
- Local power. Most of such nations have 1-3 provinces, depending on the amount of cities. They do not pose a challenge - even a strong city state can win with such power. They can have alliances and create Defense Leagues which are special treaties between nations that offer protection for smaller nations for them to be able to effectively protect themselves from stronger countries.
- Regional power. Quite large nations that control from 25 to 99 cities. They can be a tough nut to crack for local countries. On the other hand, they can form alliances and guarantee independence of smaller nations. This second option is especially useful when we want to avoid war in the given region, or have an opportune cause for war with enemy neighbors. Moreover, you receive an additional trade route in the capital and increased range of your diplomacy. The final option is threaten war, an option which will allow you to gain a city for free, provided you have evidence that the province belongs to you.
- Major power. Such countries are a quite powerful force in the region. Aside from bonuses available for major power and bigger range of diplomacy, such country can support rebels operating in other countries. This way, you increase dissent, which may lead to a revolt. Rebels are always friendly towards you and have a good relations with their sponsor. Moreover, a major power pays less for changing policies in the provinces.
- Great Power. The higher rank available, which makes a given nation a real powerhouse in every area. Has a wide range of abilities and actions. It is the only rank that can intervene in wars and stand at either side, or can enforce peace between fighting countries. As a result, such nations have a wide range of diplomatic actions unavailable for lesser nations.
It is not always recommended to increase the rank of the country. Sometimes, it is better to stay in the current rank, instead of annexing new lands. You can make conquered nations your subjects, instead of capturing new cities and provinces. This way, you'll still get new territories that are under your control, but you'll increase your income and resources without increasing your rank. In the later stages of the game, increasing the rank will be inevitable. Strengthen your country internally (economy, stability, army) and take care of foreign relations before you increase your rank.