State of war
When a state of war exists between two countries, they are officially enemies and their military forces cannot meet without battle. Each country is at war, which has certain effects unrelated to the particular enemy or enemies.
Effects of War
Being at war has effect both at home and abroad.
Effects of War on the Enemy
When a country is at war with another, their military forces will engage in battle if they meet each other. Land forces always meet if (and only if) they are in the same land province (except if one or both forces is retreating or noncombatant, or a passenger). Naval forces usually do battle if both are in the same sea zone, but they don't always meet. Naval forces cannot meet in a port, and will happily share a port with their worst enemies.
Land forces are generally unconstrained in what they do:
- They can plot moves into, and enter, the enemy country's territory. However, an army that is too small to cover an enemy province may only plot a move into it if there's an allied or enemy army already present there.
- They will loot any enemy province they are in, if not currently looted.
- They will capture trading posts and unfortified enemy settlements.
- They will cover or siege fortified enemy cities.
Finally, diplomacy between countries at war is extremely limited: the only available diplomatic actions are "Offer Peace", and a few lesser actions that will just fail.
Effects of War on Neutrals
Generally, a war between two countries has no effect for neutral third parties. However, there are a few effects:
- All Catholic or CRC countries get a casus belli against any country which is at war against the Papal States.
- A country which has claimed the title of Defender of the Faith for its particular state religion receives a casus belli against any country which is at war with any country of its faith.
Effects of War at Home
When a country is at war with any other country, there are effects on it that are otherwise unrelated to the enemy. Here is a partial listing:
- Revolt risk is raised in wrong-culture cities.
- War taxes are an available option.
- War exhaustion is usually gained, and if lost, lost at a much lower rate.
- The country gets an extra diplomat per year.
Creation of War
In general, the only way for a state of war to be created is for one country to issue a declaration of war against another. When a country revolts from another, it automatically declares war as a part of the revolt.
There is an event command ("war") which issues a declaration of war as part of an event; however there are only a handful of scripted events which use this command. Forcing a player into a war is pretty rude, and thus there is always a way to choose otherwise. No random events have the "war" command in them.
Once a war has been created, countries may enter it via joining the military alliance of the war coalition leader on either side. When a country makes a separate peace, it splits the war, creating one or two new wars.
Termination of War
A state of war can end by peace treaty, white peace, government collapse, or force annexation. On rare occasions, a state of war may also end if all countries on one side are eliminated (generally, this would be because they were forcibly annexed by a third party).
When a war ends, there are official "winners" and "losers". (This use of "winning" is just a technical one, which is why it is scare-quoted. Really winning a war means you came out ahead.) It mostly doesn't matter whether or not a country wins a war in this sense. However, there are two possible effects:
- when a country wins a war, all trade embargoes on it by any of the losers are cancelled, and cannot be re-imposed while the resulting truce lasts (5 years)
- a country must win every war to keep being Defender of the Faith.
Later in the game, it is not uncommon to fight wars against majors simply to get them to lift an embargo.
A war coalition wins a war in EU2 if it:
- got tribute, if it was the aggressing coalition
- got tribute or a white peace, if it was the defending coalition
An individual country wins a war if it is a member of a winning coalition, or if it annexes an enemy.
The cases above are all of the most typical war ends. In the case of strange war endings (govt collapse, elimination of enemy by third party) I don't know who is considered to have "won". It seems reasonable in both cases that the side that collapsed or was annexed loses.