Certain AI-controlled countries are defined ingame as antagonists, who get special modifiers that makes these nations significantly stronger, more aggressive, and more likely to grow into a large and powerful empire capable of providing a significant challenge to the player. These are usually countries that were historically successful or punched above their weight during the time period.
Antagonist status is fixed at the beginning of the game and is AI-only - if a human player takes control of a country that would normally be an antagonist, whether starting the game as that country or switching with the console, the antagonist modifier will be removed.
Antagonist status is given to the following countries at the start of the game, if they are AI-controlled:
Antagonist status is tied to the country itself, not to the tag. If an antagonist country forms a new nation, or is annexed and then released, it will keep its antagonist status; similarly, forming a nation that begins with antagonist status will not make that country an antagonist.
All antagonists get the following modifiers:
In addition, antagonist nations will get a 25% bonus to all AI difficulty modifiers on hard, and a 50% bonus to all AI difficulty modifiers on very hard. Antagonist countries also receive hidden dice roll bonuses in combat against other AI-controlled countries and a bonus when negotiating peace deals against other AIs.
Antagonists are also significantly more aggressive than other AI-controlled countries, and so they will likely grow to a significant size if they are not checked early in the game.