I think espionage should be made relevant in some form for the entirety of the game. Why should any civ get (for free) statistics showing you who has the most powerful military / scientific output / religious output?
These should be hidden behind espionage walls, with increasing specialisation required to maintain a flow of information. Want to know if Scythia is as strong as you fear? Better have a spy in their lands (separate point: sending a spy to another Civ generally without targeting a specific city should be an option for more general missions) otherwise you'll just have to scout it out yourself.
The number of available spies should be drastically increased, but also hidden behind cultural policy barriers. Would also be interesting to have additional spies from one or more governments.
Additional missions which could make the system more dynamic:
Spread propaganda (war, available from classical era): Choose a target rival Civ. If successful, the Civ in which your spy operates will feel significant pressure to declare war on that Civ. Each turn that the pressured Civ does not declare war on the chosen rival, there is a chance to increase the required amenities of every city in their civilization by 1. Upon declaring war this penalty is immediately lost, but peace may not be declared for 20 turns. If a civilization affected by propaganda has not declared war on the civ they are pressured to but is instead declared war on by said civilization, each city in their empire will suffer a permanent +1 amenity requirement.
Example: Germany uses spread propaganda on France, attempting to elicit a war between France and England. The mission succeeds. For 30 turns, at the start of every turn there is a chance France will suffer an empire-wide amenity penalty if they haven't declared war on England. If France declares war on England the penalty is lost but no peace may be declared for 20 turns. If however England declares war against France first, France will now permanently have a +1 amenity penalty (previous penalties from the start of turn are negated).
Spread fanaticism (religion, available from classical era): Attempt to promote religious intolerance in any civ which has founded its own religion. If successful, target civ gains a point of religious fanaticism. Fanaticism points cannot be removed by a player. If a player with at least 3 fanaticism points has their religion eliminated from the game, rebels will spawn periodically near their cities for the remainder of the game.
At 3 points, anytime a civ's city is converted to a foreign religion, rebel fighters will spawn near the converted city until it is returned to the home religion.
At 6 points, any city within the civ's empire which has more than one religion present will suffer an amenity loss equal to each additional religion beyond the founded religion.
At 9 points, target civ's citizens will occasionally demand production of holy site works (or a shrine), not allowing the player to select what to produce.
At 12 points, target civ's citizens will have a reasonably high chance to "reject" scientific discovery. Upon researching a new technology, if your citizens reject it your research points will instead be returned to zero and you will not have that technology.
At 15 points, target civ is permanently at war with all other civs who founded a religion. Capturing enemy cities other than the capital are always razed as a sacrifice to the civ's god(s). Capturing a capital reduces it's population to 1 as the civ's fanatics purge the city of heathens. If the fanatical civ has not killed an enemy unit or taken an enemy city in the last 15 turns, disgruntled rebels will appear within the civ's borders until this is done.
Assassinate senator (martyr, available from ancient era): Send one of your spies on a suicide mission to assassinate a leading politician of a civ. If successful, target civ loses control over their civilization for 10 turns. All units and production queues are moved / selected automatically. Spy dies whether successful or not.
Disrupt communications (war, available from industrial era): Attempt to decipher and disrupt enemy communications. If successful, target civ loses control of their military units outside of their borders for 15 turns, and 5 turns for units within their borders. Moving a unit back within their border will not affect the number of turns of lost communication (i.e. a unit with 14 turns left who crosses into a target civ's home borders will not reduce down to 5 turns). Takes 25% less time to complete than assassinate senator, and spy does not die if successful.
Spread pseudoscience (tactical, available from renaissance era): Select a resource. Attempts to persuade the public in a target civ that this resource is toxic, dangerous or morally reprehensible. If successful, target civ can no longer make use of this resource unless a mission is successfully completed to remove the pseudoscience. Missions to remove pseudoscience take 25% longer than the original mission, and civilizations who do not possess the ability to spread pseudoscience cannot undertake a counter mission.
Assess civilization (tactical, available from ancient era): Select a civ. Send your spy to their capital, where they will attempt to discover the status of the country: gold, science and faith output per turn; military strength; current wars; number of technologies researched; current production in the capital. This mission is always successful, but takes a long time to complete. When completed you will received a "point in time report" which will update automatically for 3 turns, after which the information will become more and more obsolete. The mission can be sped up by: 1) promotions, 2) cultural policies and 3) using the same spy in the same civilization for multiple assessments. Each time the same spy completes an assessment mission on the same civ, the required mission time is reduced by 3%, up to a maximum of 33% reduction.
Black ops mercenaries (tactical, war, available from modern era): Attempt to train some of your military units to become stateless. If successful, select up to five units. These units will appear to all other players as stateless barbarians, but you will maintain full control over them. Attacking another civ will not result in war being declared against that civ when using one of these units. Multiple spies can complete this mission at the same time, but a civ may not sustain more than 10 stateless units at one time.
Study offensive tactics (tactical, war, defensive, available from industrial era): Attempt to study the offensive capabilities of a target civ. If successful, for the next 30 turns you will receive the following benefits against units of that civ: +10 combat strength within your own borders; +6 city combat strength; -10 combat strength to their units within three tiles of one of your cities.
Study defensive tactics (tactical, war, offensive, available from industrial era): Attempt to study the defenses of a target civ. If successful, for the next 30 turns you will receive the following benefits against that civ: city walls no longer need to be destroyed. Cities take direct damage from your attacks and can be taken without needing to first reduce a wall's health to 0.
Turncoat (tactical, espionage, available from renaissance era): Attempt to convert a captured rival spy to your civilization. If successful, target civ permanently has one less spy capacity, and your civ permanently gains one spy capacity. All spies of the target civ operating in your borders following a successful turncoat operate at one level lower than normal (does not stack). Turncoat may only be attempted by a spy of a higher rank than the captured spy.
Hiroshima plan (tactical, martyr, nuclear war, available from modern era): Select target civilization which possesses at least one nuclear bomb which is above water. If successful, your spy will set the nuclear bomb to detonate on one of their own cities. The city choice is based on population- the higher the population, the more likely the city will be the target of the nuclear bomb. If successful your spy will die from radiation poisoning.
Tea and Battleships (tactical, naval warfare, available from renaissance era): Attempt to emulate the naval successes of the British Empire by using superior naval tactics. If successful, for the next 30 turns your civilization will receive the following benefits: +1 movement to all naval units. Naval units may move after attacking. +1 vision to all naval units. Naval units may heal outside of friendly territory at half the usual rate. Only one civ may benefit from this mission at any one time, and a notification of when this mission begins and ends is displayed to all other civs because your navy can't stop boasting at port.
Mastery of the craft (tactical, espionage superiority, late game, available from modern era): If your civilization has successfully completed every mission at least once, you gain access to the following benefits:
+3 additional spies (instant, does not need to be built, permanent capacity increase)
Access to three elite missions:
Cultural superiority (elite, end game): Attempt to assert your cultural dominance. If successful, you gain the following benefits as long as no other civ produces more culture per turn than you:
+1 combat strength to all units for every great artwork, writing, or music
+2 movement for units starting within your borders
War weariness is tripled for civs who are at war with you.
This bonus is permanent once the mission is completed.
Magnum opus (elite, end game): Attempt to found the most sophisticated intelligence network the world has ever seen. If successful, you gain the following benefits:
All technologies which are researched by any civ which you do not have instantly become yours as well. You permanently have access to all of a civ's stats (military, faith, gold production et al) and your civ permanently has both the offensive and defensive tactics missions in effect against all rival civilizations.
Radiation poisoning (elite, end game): Attempt to poison another civ's leader. The chance of success is small, but multiple spies can attempt the same mission at the same time. If successful, target civ instantly loses and their cities and units become barbarians. A message box appears upon completion of this mission, allowing you to type a short farewell message to your soon to be dead rival which will appear at the start of their last turn.
Sorry for the long read guys, but I just started typing and.. well...
Anyways let me know what you think! Espionage could be SUCH a fun element to Civ if expanded massively
These should be hidden behind espionage walls, with increasing specialisation required to maintain a flow of information. Want to know if Scythia is as strong as you fear? Better have a spy in their lands (separate point: sending a spy to another Civ generally without targeting a specific city should be an option for more general missions) otherwise you'll just have to scout it out yourself.
The number of available spies should be drastically increased, but also hidden behind cultural policy barriers. Would also be interesting to have additional spies from one or more governments.
Additional missions which could make the system more dynamic:
Spread propaganda (war, available from classical era): Choose a target rival Civ. If successful, the Civ in which your spy operates will feel significant pressure to declare war on that Civ. Each turn that the pressured Civ does not declare war on the chosen rival, there is a chance to increase the required amenities of every city in their civilization by 1. Upon declaring war this penalty is immediately lost, but peace may not be declared for 20 turns. If a civilization affected by propaganda has not declared war on the civ they are pressured to but is instead declared war on by said civilization, each city in their empire will suffer a permanent +1 amenity requirement.
Example: Germany uses spread propaganda on France, attempting to elicit a war between France and England. The mission succeeds. For 30 turns, at the start of every turn there is a chance France will suffer an empire-wide amenity penalty if they haven't declared war on England. If France declares war on England the penalty is lost but no peace may be declared for 20 turns. If however England declares war against France first, France will now permanently have a +1 amenity penalty (previous penalties from the start of turn are negated).
Spread fanaticism (religion, available from classical era): Attempt to promote religious intolerance in any civ which has founded its own religion. If successful, target civ gains a point of religious fanaticism. Fanaticism points cannot be removed by a player. If a player with at least 3 fanaticism points has their religion eliminated from the game, rebels will spawn periodically near their cities for the remainder of the game.
At 3 points, anytime a civ's city is converted to a foreign religion, rebel fighters will spawn near the converted city until it is returned to the home religion.
At 6 points, any city within the civ's empire which has more than one religion present will suffer an amenity loss equal to each additional religion beyond the founded religion.
At 9 points, target civ's citizens will occasionally demand production of holy site works (or a shrine), not allowing the player to select what to produce.
At 12 points, target civ's citizens will have a reasonably high chance to "reject" scientific discovery. Upon researching a new technology, if your citizens reject it your research points will instead be returned to zero and you will not have that technology.
At 15 points, target civ is permanently at war with all other civs who founded a religion. Capturing enemy cities other than the capital are always razed as a sacrifice to the civ's god(s). Capturing a capital reduces it's population to 1 as the civ's fanatics purge the city of heathens. If the fanatical civ has not killed an enemy unit or taken an enemy city in the last 15 turns, disgruntled rebels will appear within the civ's borders until this is done.
Assassinate senator (martyr, available from ancient era): Send one of your spies on a suicide mission to assassinate a leading politician of a civ. If successful, target civ loses control over their civilization for 10 turns. All units and production queues are moved / selected automatically. Spy dies whether successful or not.
Disrupt communications (war, available from industrial era): Attempt to decipher and disrupt enemy communications. If successful, target civ loses control of their military units outside of their borders for 15 turns, and 5 turns for units within their borders. Moving a unit back within their border will not affect the number of turns of lost communication (i.e. a unit with 14 turns left who crosses into a target civ's home borders will not reduce down to 5 turns). Takes 25% less time to complete than assassinate senator, and spy does not die if successful.
Spread pseudoscience (tactical, available from renaissance era): Select a resource. Attempts to persuade the public in a target civ that this resource is toxic, dangerous or morally reprehensible. If successful, target civ can no longer make use of this resource unless a mission is successfully completed to remove the pseudoscience. Missions to remove pseudoscience take 25% longer than the original mission, and civilizations who do not possess the ability to spread pseudoscience cannot undertake a counter mission.
Assess civilization (tactical, available from ancient era): Select a civ. Send your spy to their capital, where they will attempt to discover the status of the country: gold, science and faith output per turn; military strength; current wars; number of technologies researched; current production in the capital. This mission is always successful, but takes a long time to complete. When completed you will received a "point in time report" which will update automatically for 3 turns, after which the information will become more and more obsolete. The mission can be sped up by: 1) promotions, 2) cultural policies and 3) using the same spy in the same civilization for multiple assessments. Each time the same spy completes an assessment mission on the same civ, the required mission time is reduced by 3%, up to a maximum of 33% reduction.
Black ops mercenaries (tactical, war, available from modern era): Attempt to train some of your military units to become stateless. If successful, select up to five units. These units will appear to all other players as stateless barbarians, but you will maintain full control over them. Attacking another civ will not result in war being declared against that civ when using one of these units. Multiple spies can complete this mission at the same time, but a civ may not sustain more than 10 stateless units at one time.
Study offensive tactics (tactical, war, defensive, available from industrial era): Attempt to study the offensive capabilities of a target civ. If successful, for the next 30 turns you will receive the following benefits against units of that civ: +10 combat strength within your own borders; +6 city combat strength; -10 combat strength to their units within three tiles of one of your cities.
Study defensive tactics (tactical, war, offensive, available from industrial era): Attempt to study the defenses of a target civ. If successful, for the next 30 turns you will receive the following benefits against that civ: city walls no longer need to be destroyed. Cities take direct damage from your attacks and can be taken without needing to first reduce a wall's health to 0.
Turncoat (tactical, espionage, available from renaissance era): Attempt to convert a captured rival spy to your civilization. If successful, target civ permanently has one less spy capacity, and your civ permanently gains one spy capacity. All spies of the target civ operating in your borders following a successful turncoat operate at one level lower than normal (does not stack). Turncoat may only be attempted by a spy of a higher rank than the captured spy.
Hiroshima plan (tactical, martyr, nuclear war, available from modern era): Select target civilization which possesses at least one nuclear bomb which is above water. If successful, your spy will set the nuclear bomb to detonate on one of their own cities. The city choice is based on population- the higher the population, the more likely the city will be the target of the nuclear bomb. If successful your spy will die from radiation poisoning.
Tea and Battleships (tactical, naval warfare, available from renaissance era): Attempt to emulate the naval successes of the British Empire by using superior naval tactics. If successful, for the next 30 turns your civilization will receive the following benefits: +1 movement to all naval units. Naval units may move after attacking. +1 vision to all naval units. Naval units may heal outside of friendly territory at half the usual rate. Only one civ may benefit from this mission at any one time, and a notification of when this mission begins and ends is displayed to all other civs because your navy can't stop boasting at port.
Mastery of the craft (tactical, espionage superiority, late game, available from modern era): If your civilization has successfully completed every mission at least once, you gain access to the following benefits:
+3 additional spies (instant, does not need to be built, permanent capacity increase)
Access to three elite missions:
Cultural superiority (elite, end game): Attempt to assert your cultural dominance. If successful, you gain the following benefits as long as no other civ produces more culture per turn than you:
+1 combat strength to all units for every great artwork, writing, or music
+2 movement for units starting within your borders
War weariness is tripled for civs who are at war with you.
This bonus is permanent once the mission is completed.
Magnum opus (elite, end game): Attempt to found the most sophisticated intelligence network the world has ever seen. If successful, you gain the following benefits:
All technologies which are researched by any civ which you do not have instantly become yours as well. You permanently have access to all of a civ's stats (military, faith, gold production et al) and your civ permanently has both the offensive and defensive tactics missions in effect against all rival civilizations.
Radiation poisoning (elite, end game): Attempt to poison another civ's leader. The chance of success is small, but multiple spies can attempt the same mission at the same time. If successful, target civ instantly loses and their cities and units become barbarians. A message box appears upon completion of this mission, allowing you to type a short farewell message to your soon to be dead rival which will appear at the start of their last turn.
Sorry for the long read guys, but I just started typing and.. well...
Anyways let me know what you think! Espionage could be SUCH a fun element to Civ if expanded massively
