There are several major powers (as well as lesser countries), that may be created via scripted events from other countries during play. This page lists the countries that can be formed from others in vanilla EU2, and shows the preconditions for the event to form them. Although there are distinct events for each country formation, one thing they all have in common is that the country being formed must not currently exist.
Provinces are referred to by their province name, but also their province number. (In events files, the province number is what is used.) For reference to province numbers, see Maps_with_the_IDs_of_provinces_on_them.
Conditions: Muscovy can transform to Russia whenever after 1st January 1520 if it owns a combination of the following three:
Vologda (268) or Nizhgorod (272),
Ryazan (448) or Vladimir (271) or Novgorod (274) or Pskov (277) or Tver (278)
It is 1526. If Muscovy owns Muscow, Nizhgorod and Tver it can become Russia. If it owns Muscow, Vladimir and Pskov, it cannot.
Other Russian countries
Countries: Countries that can become Russia apart from Muscovy are: Novgorod, Pskov, Ryzan, Suzdal and Tver.
Conditions: After 1520 they have to own their capital, Moscow and the capital of one of the other Russian minors (Novgorod, Vologda, Nizhgorod, Ryazan, Vladimir, Pskov or Tver).
Countries: Brittany, Navarre, Provence, Auvergne, Orléans, Bourbonais, Flanders.
Conditions: One of these countries has to own Ile De France before 1515 and France must not exist. Navarre, unlike the others has till 1575 to meet the conditions to become France.
Countries: Castille, Aragon.
Conditions: If Spain does not exist and either of these countries holds Castille (436) between 1476 and 1490, it can become Spain.
Conditions: Both Prussia and Brandenburg must exist at some time between 1615 and 1700. If it is true, Brandenburg gets 'Prussian incorporation' event. Then, after 1st January 1701, Brandenburg gets the option to become Prussia if it holds the province of Prussia (290).
Countries: Trebizond, Hellas.
Conditions: One of these countries has to be Orthodox, own Constantinople (357) and must not be at war. Of course, Byzantium must not already exist.
Conditions: Manchu has to control Beijing (649) after 1st Jan 1683 (and China must not already exist).
Conditions: China has to choose option B in “The fall of the Ming Dynasty” on the 25th of April 1644. This triggers an event for the Manchu, "The Takeover of China", where they have to choose option A. After this China will get two events, the first will allow them to inherit Manchu, the second will change China into Manchu.
Note: This event series relies on the Manchu ai to pick option A, there is a small possibility that they will pick option B which will ruin the event sequence. Moreover China is then given an event to either surrender to Manchu or give away large parts of China to them and become their vassals
Countries: Teutonic Order.
Conditions: Between 1560 and 1562, Poland, Sweden, Denmark and Russia must exist and Courland cannot.