In >BLOC, espionage involves secretive operations that reveals enemy secretive information as well as supporting the rebels or opposition, or just counterintelligence. To perform espionage, you must have at least 1 secret agent.
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Secret agents are agents that work for the intelligence agency and can infiltrate enemy ground, provide aid to opposition or rebels, and perform counterintelligence. Each spy costs 500k in cash and can be purchased in Foreign Policy page. You must have 1 secret agent in order to perform espionage, and you can have up to 3 as of current version of >BLOC.
How espionage works
Espionage in other nations
In order to perform espionage in other nation, you must send your spy to the target country and have it successfully infiltrated into another country. Once entered, you can provide aid to opposition, which will reduces the country's approval, or aid in the rebels, which will reduce stability.
This button allows a special agent to infiltrates the enemy ground allowing covert actions. There is a low chance of the agent being captured and executed. Doing so keeps you from returning/sending a spy from/to a country or perform counterintelligence for the rest of the turn.
Aiding opposition costs 100k in cash and reduces the target's leader's approval.
Aid the rebels
Aiding the rebels raises rebel threat by 1 level, which reduces the target's stability. It costs a crate of weapons to do it and there is 50% chance the weapon is seized at the border. Doing so will in the long run reduces stability to a level where a rebellion happens. It is known that rebels don't need to be present in order for this to work.
Withdraw special agent
As simple as that. Your spy will return the country intact, but you are kept from returning/sending a spy from/to a country or perform counterintelligence for the rest of the turn.
The key risk is that your spy is KIA while performing espionage in another country just because the target country's IA have successfully performed counterintelligence!
Counterintelligence (Espionage inside your country)
Again, you need a spy and that the agency is not busy sending/returning spies. To perform counterintelligence spend 100k in cash in Foreign Policies page. Once you've performed counterintelligence, either your special agent failed to hunt down any spies, or you got one of the spy (but you always fail if there's no rival spy in your country); after that you are not able to send/return a spy to/from a country or perform counterintelligence again for the remainder of the turn. There is 50% chance to catch each spy in your nation.
Are spies worth it?
As a matter of fact, yes. Spies can do great dents to stability and approval, while taking enemy spies out. You definitely do not want this to happen: an underdog who is on the verge of defeat only to pull off an upset victory after the aggressor's country is ravaged by a revolution that was created in part by spies working for the underdog's IA.