Diplomatic actions

Diplomatic actions are actions that are performed by some special unit types (typically, Diplomat or Spy, maybe other in another rulesets). Some of them are hostile and may be performable even out of war time (but if you do so, don't be surprized that the war will come soon and negotiating a treaty will be uneasy - all hostile actions are noticed and may be presented to a Senate as casus belli).

Some actions consume the actor, some other ones may grant him or her a veteran status (that helps to survive further actions). Many of the actions can fail more or less probable, then the acting unit will be captured and executed; even if the action has succeeded and does not consume the actor, there is still a chance to be captured on return. The basic chance of both performing and escaping is set in a game variable, for escaping, it then can be modified by the spy's veteran bonus over the basic level, and for performing success, by target effect "Action_Odds_Pct".

Diplomatic defense

If a hostile action is performed against a tile where there is one or more another units with diplomatic capability, the action does not take place (infiltration failed), and a diplomatic battle occurs. (In some newer Freeciv version, this is not applied to one Diplomate bribing the another, before it resulted in just one of them dying). Either the attacker or the defender will be defeated and destroyed, and the other side may become a veteran; its health will not suffer but the battle will take 1 movement point from the attacker. Diplomatic strength is not influenced by "tired attack" setting. Rules of the battle:

A unit with "SuperSpy" flag (Leader, Barbarian Leader) always wins unless attacking another SuperSpy; in a battle of two SuperSpies the attacker loses. Note that the flag itself does not enable diplomatic actions, only defends from them.
Basic attacker's chance is 50%.
A unit with "Spy" flag has 25% higher chances.
Chances of a unit are increased by its veteranship combat bonus. Usually diplomatic units have their own veteranship system, it's not recommended to set such bonuses more than 20%. The difference of the bonuses is added to the attacker's chance.
Finally, the chances of the attacker are reduced on a portion of them defined by "Spy_Resistant" effect value of the defender's tile (the defending unit itself is not important for the effect), and the dices are rolled.

I. e. if a Diplomat attacks similar one, he wins 50% cases, but if the defender is in a city with resistant effect 25%, then the attacker's chance is only 50-[50×25/100] = 38%.

Consequences and common limitations

General requirements for a diplomat to perform any action:

Freeciv 2.5

Movement points left (at least one fragment);
Target must be on the same tile, or adjacent;
Diplomat must be on a native tile.

Freeciv 2.6

Unit target must be seen;
City target tile must be known;
Action must be enabled.

After some missions, if they are performed successfully, an actor with "Spy" flag may be either captured and executed (diplomat's owner loses the unit, nobody has units killed number increased) or escape to the closest own city (if home civ has no cities, no option to escape) with no movepoints but a probability of rising in its rank. Probability of escaping is basic diplochance plus difference in power factors between 0th and the current veteran levels; units with both "Spy" and "SuperSpy" flags always escapes if there is any city owned.

City actions

Establish Embassy

Always successful, the actor-consumption is ruleset-dependent in newer versions.

Either a Diplomat or Spy can establish an embassy (in civ2civ3, also an Explorer).
Barbarians always execute ambassadors.
Otherwise, the embassy is created.
It costs some minimal movement to establish an embassy.
Diplomats are consumed in creation of embassy.
Spies always survive.

Investigate City

Performability and actor consumption depend on ruleset in newer versions.

Either a Diplomat or Spy can investigate a city.
Allowed against all players.
It costs some minimal movement to investigate a city.
Diplomats die after investigation.
Spies always survive.

Sabotage City

Either a Diplomat or Spy can sabotage an enemy city.
The players must be at war
Wonders (or anything with sabotage=0) can't be sabotaged.
The saboteur tries to infiltrate the city.
Check for basic success. The saboteur may not survive this.
Determine target, given arguments and constraints. The target may be current city production or a building in the city (not a wonder). Spies can try for a specific target (but if you not allow them to choose themselves it halves the basic success chance), Diplomates always sabotage random thing (that is 50% to be the production if there are any buildings at all and at least one production point in the city stock).
If you try for a random target and none is found, you get a message about this and your diplomat loses so many movement points as were needed to move onto the city tile.
If specified, city walls and anything in a capital are 50% likely to fail (the chance is the building's sabotage property minus "Building_Saboteur_Resistant" effect).
Do sabotage!
A Diplomat will be captured and executed.
A spy may be captured and executed, or escape to closest own city.

Steal Technology

Surely, the targeted player must have an advance the stealer does not know. In Longturn games, the basic probability of success of this action is controlled by a separate server option (usually it is considerably lower than the basic succes probability).

Either a Diplomat or Spy can steal a technology.
Spies can select which technology to steal.
Check for infiltration success. Our thief may not survive this.
Check for basic success. Again, our thief may not survive this.
If a technology has already been stolen from this city at any time:
- Diplomats will be caught and executed.
- Spies will have an increasing chance of being caught and executed.
Steal technology!
A spy may be captured and executed, or escape to closest own city.

Incite a Revolt

Either a Diplomat or Spy can incite a city to disaffect.
Can't incite a city to disaffect if:
- Owner runs an unbribable government (e.g., democracy).
- Player doesn't have enough gold.
- You are allied with the city owner.
Check for infiltration success. Our provocateur may not survive this.
Check for basic success. Again, our provocateur may not survive this.

If successful, the city will disaffect:

Player gets the city.
Player gets the city's present units and the supported units within one square of the city.
Player steals a technology advance, if any were unknown (in Longturn games this is patched off).
City loses 1 pop (but size 1 city remains).
A Diplomat will be captured and executed.
A Spy may be captured and executed, or escape to closest own city (that is the incited city)

Poison City

If successful, reduces population by one point.

Only a Spy can poison a city's water supply.
Only allowed against players you are at war with.
Check for infiltration success. Our poisoner may not survive this.
Only cities of size two and larger may be poisoned.
The poisoner may be captured and executed, or escape to closest own city.

Steal Gold

New in 2.6: if success, you can have some portion of the player's treasury (but the thief can take part of it for her own). Since 3.0, possibility of escaping is ruleset-controlled.

Steal maps

New in 3.0: Steals like half of the target player's maps, tiles are scattered with no pattern. Escape possibility is ruleset-controlled.

Suitcase Nuke

New in 3.0: KABOOM! If your spy is not caight, she escapes the blast if it is allowed by the ruleset.

Spread Plague

New in 3.1: Atishoo! Atishoo! We all fall down. Triggers a plague in the target city. The plague may spread naturally along trade routes if illness is enabled in the ruleset.

Unit actions

Bribe Unit

Either a Diplomat or Spy can bribe an other players unit.
Can't bribe a unit if:
- Owner runs an unbribable government (e.g., democracy), or by other means has nonzero "Unbribable_Units" effect.
- Player doesn't have enough gold.
- It's not the only unit on the square (in newer versions, not in all rulesets)
- You are allied with the unit owner.
- The unit is unique and the bribing player already has one such.
Otherwise, the unit will be bribed.
A successful briber will try to move onto the victim's square. If it is impossible, the briber's movepoints are zeroed.

Cost of bribing a unit

cost = gold of unit owner + base bribe cost (default= 750)
cost = cost / (distance to unit owner capital(max 32) + 2)
cost = cost * (shield cost / 10)
cost = cost + effect "Unit_Bribe_Cost_Pct"% (was hardcoded in v.2.5 that if settler: cost = cost/2)
if veteran: cost = cost + 33%(or another veteran power factor)
- cost = cost + cost * veteran move_bonus / unit move_rate(if 0, single move) [in fragments]
cost = cost/2 + (cost/2) * current health / full health

Note that units with very low shield costs will be free to bribe.

Sabotage Enemy Unit

If successful, reduces hit points by half of those remaining. If target unit has only 1 hp, in v.2.5 the action is impossible, but in v.2.6 and later may be enabled by the ruleset (then the unit dies; in standard rulesets, not enabled). The following limitations are hard in v.2.5 but become ruleset-controlled in newer versions:

Only a Spy can sabotage an enemy unit.
Only allowed against players you are at war with.
Can't sabotage a unit if:
- It has only one hit point left.
- It's not the only unit on the square.
The action may cause a diplomatic incident.
The saboteur may be captured and executed, or escape to closest own city.

Spy Attack

New in 3.1: Fight a diplomatic battle against a diplomatic defender on the target tile.