外交

在很大程度上，钢铁雄心4的外交是双边的，这意味着所有的关系、提议和请求都是一对一的，发生在玩家和目标国家之间或者两个AI国家之间。但有一个例外是，当一个阵营被创建时。这个阵营的所有成员国都将一起参加防御战争，也可以邀请其他阵营成员国和侵略者一起参加侵略战争。 此外，外交并不是对等的。这意味着，影响另一国的关系或接受请求的可能性的所有变量对每个国家都是完全独立的。例如，玩家国家可能与另一个国家有正面关系，而这个国家却可能与玩家有负面关系。外交关系可以通过处于同一阵营、属于同一意识形态, 保障独立,贸易或者改善关系来增进。

外交行动 

游戏中有许多外交行动。下表中的所有外交行动都是基本行动，所有可取消的行动都有一个相关的外交行动，一旦采取基本行动，这些行动就变得可用，它也将取代外交列表中的基本行动。唯一的例外是“派遣远征军”，可以被“撤回远征军”取消；还有“接管占领区”，可被“移交占领区”所取消。

外交行动	说明	要求	取消条件
宣战	发动一场新战争的唯一途径	在目标国拥有有效的战争目标	战争持续时间超过6个月。 必须是阵营领袖。 必须是战败的一方 胜方的战争分数至少为50%
正当化战争目标	开始正当化对另一个国家的战争目标。	目标国家不能是盟友。 花费一定数量的. 点数花费会随着世界紧张度 世界紧张度 的增加而减少，花费也受颠覆活动修正影响。 最少需要花费2.	无
保障独立	保证另一个国家的独立。如果任何人对一个被保障国宣战，该被保障国将自动加入保障国的阵营。	目标国家也有同样的意识形态。. 花费25 每多保障一个国家都会使成本+25 世界紧张度 世界紧张度 达到要求的阈值	无
召唤盟友	召唤一个盟友参加本国的战争	目标国家与本国必须是一个阵营中的成员	无法取消
要求军事通行权	军事通行权允许本国军队通过另一个国家的领土，无论是否结盟。军事通行权将会自动授予同一阵营的成员国。	必须得到目标国家的接受	目标国领土上没有本国军队。
提供军事通行权	给另一个国家提供军事通行权。如果该国接受，并不会自动授予你军事通行权	必须得到目标国家的接受	目标国家在被允许进入的国家领土上没有军队
请求驻港权	驻港权允许船只进入另一个国家的港口，不管是否结盟。驻港权将自动授予同一阵营的成员国。	必须得到目标国家的接受	无
给予驻港权	向另一个国家提供驻港权。如果该国接受，并不会自动授予你驻港权。	必须得到目标国家的接受	无
Improve relations	Start improving relations between you and the target country up to +100 over time. Relation affects trade influence and the success likelihood of other diplomatic actions.	Must not be at war with target country. Costs 10 +0.2/day if both countries have the same ideology and +0.4/day with differing ideology.	None
Send Attaché	Sends an attache to a country. This gives the sender additional 陆军经验 and 战争支持度. They can also see the receiver's military positioning.	DLC required. Target must be at war. 100 to send the attache. 50 command power is used to maintain the attache.	None.
Non-aggression pact	Having a non-aggression pact (NAP) disables "Justify War goal" and "Declare war" diplomatic actions.	Target country must accept.	Not cancellable without having a common border or within the first 12 months of the pact. After 12 months, the ability to break a NAP will depend on the relative size of armies along the common border. Up to 18 months past the NAP, the country will require a 2:1 ratio of troops compared to its opponent on the common border. Between 18 and 24 months, a 1:1 ratio is required. Past 24 months after the NAP, a 1:2 ratio is required to break the pact. NAPs dissolve after four years.
Invite to faction	Invite another country to your faction.	Target country must accept Requires popularity of inviting country's ideology > 30%	Must not be faction leader. Must not be in war with other faction members. Three months must pass between a country joining a faction and them being kicked.
Request License Production	Licenses equipment from target country, allowing you to produce target equipment and research target technology faster. Civilian factories are used to pay for license.	Target country must accept. 玉碎瓦全 is required.	Two months minimum must pass before a license can be cancelled.
Create faction	If you are not already in a faction and a National focus allows you to create a faction, you may invite another country to create a new faction.	Same ideology. Target country must accept.	Must not be faction leader. Must not be in war with other faction members.
Join faction	Allows you to join a faction. Will automatically join existing war(s).	Target country must be faction leader. Must not be in a faction.  World Tension threshold reached. Faction leader must accept.	Must not be in war with other faction members. May not Leave Faction if already in a war as part of the faction.
Start Lend lease	Send any equipment to another non-enemy country currently at war. It's possible to send a single shipment of a specified amount, or set a specified monthly amount or percentage of monthly production to be sent. Shipments occur once per month and information on past and present shipments is available in a tooltip for the Lend-Lease section at the top of the Recruit/Deploy window.	Target country must have enough convoys to receive the equipment, unless there's an unobstructed land path.  World Tension threshold reached.	None. Click on the Lend Lease action to modify or cancel Lend Lease instructions.
Request lend lease	Ask a country to send lend-lease of specific equipment archetypes. The selection screen shows the stockpile and production rates of the target country.	Requires 共赴胜利. Target country must accept. Must be at war.	None
Join wars	Allows you to join the war of another faction member.	Must not already be in war with allies. Target country must be faction leader.	Not cancellable
Send Volunteers	Send a limited number of divisions to a country. Control over the units is retained, but return only when donor is at war.	Target country must be at war. Must be at peace. Must not be in the same faction as the target country. Total number of divisions threshold reached.  World Tension threshold reached.	None
Expeditionary Force	Send an unlimited number of divisions to a fellow member of the faction. Control over the units is transferred.	Must be fighting a war together. Target country must be an ally. Target country must accept. Divisions must be on land.	Donor must activate Return Expeditions to recover Divisions. A target country Disband order to Expeditions returns them to donor.
Return Expeditions	Recovers control over all units currently sent as Expeditionary force to the target country.	None	None
Request forces	Gives control over a selected number of divisions that are part of the military of the target country.	Target country must be our puppet.	A Disband order to the requested forces returns them to the puppet.
Boost party popularity	Increases the popularity of the target country's local party with the same ideology. With La Resistance enabled, this diplomatic action is moved to a mission an operative can do.	Costs 0.25 per day	None
Stage a coup	Starts preparations for a Coup d'État in the target country. The most common effect is to start a civil war in the country. The result of this action will depend on the popularity of the political party belonging to your ideology. With La Resistance enabled, this diplomatic action is moved to an operation.	200 or more, accumulating at a maximum rate of 0.50 per day. This cost is modified by Subversive Activities modifiers. Thousands of infantry equipment.	None
Ask for control of state	Ask current controller of an occupied State to give up control.	Must be in a war together. Must have sufficient war contribution. Target country must accept. Target State must not be considered a Core of the target country.	Can (in theory) be canceled through the "Give control of state" action. Otherwise not cancellable.
Give control of state	Give control of one or multiple occupied States.	Target country must accept.	Can (in theory) be canceled through the "Ask for control of state" action. Otherwise not cancellable.
Reduce subject autonomy	Reduces a subject's autonomy level.	The subject's autonomy is low enough to be reduced a level. Can afford the 政治点数 cost.	Cannot be cancelled.
Request Garrison support	Ask a puppet or faction member to provide manpower to fill garrisons.	Target country must accept.	None.

Additional information

• Military Access: You don't need to give another country access to your own territory if both you and the second country are at war with a common enemy. For example, if the USA, UK and Soviet Union are all at war with Germany, then the Soviet Union will have access to UK and US territory to attack/defend against Germany while the UK and USA will have access to any territory controlled by the Soviet Union. This automatically happens when warring nations gain common enemies and cannot be prevented in any way.
• Guarantee independence: The  political power cost will start at 25 for the first guarantee and will then increase by 25 for every subsequent guarantee, in the following fashion: 50 for the second, 75 for the third, 100 for the fourth and so on.
• Join faction and Create faction: the conditions to cancel these diplomatic actions are essentially the same. They're the conditions to activate the Leave faction diplomatic action, except that you cannot be the faction leader when you join a faction. The tooltip does not warn you, but if you go to war along with the faction then you may not leave it, so Leave Faction is timely in the event of a Call to Arms.
• Start Lend Lease: the amount of production that can be sent to the target country can be a fixed number of units out of the monthly production or a percentage of the monthly production, but not both at the same time. It's possible to modify the Lend lease at will. For further discussion of Lend Lease, refer to the Equipment section.
• Stage a Coup: This diplomatic action also requires to select the State of origin of the civil war. At the onset of the civil war, the rebelling State will be joined by a number of other States, the number of which will vary based on the proportional party popularity when the full political power requirement is filled. For this reason, Stage a Coup is more effective when combined with "Boost party popularity" to well over 50%. The amount of infantry equipment required appears to be a function of the target country's civilian population. The more populous the country, the more infantry equipment a nation has to give in preparation for the civil war. Coups will automatically succeed with over 40% party popularity if performed in a country with only one state. Otherwise a successful coup will start a civil war. For further information about civil wars, refer to the Civil War article.

世界紧张度 

主条目：World tension

 World Tension acts as a measurement of how close the game is to become a world war. Many diplomatic actions are limited by world tension. Annexing countries, joining factions, declaring war on nations are all examples of things that increase world tension.

Generally speaking, 轴心国 powers want the world tension to stay low so they do not get a massive coalition against them, while democracies like the 美国 may want world tension to increase so that they can intervene.

When world tension is high, a country that has war declared upon it is likely to accept an offer to join from a faction of the same ideology.

机制 

事件与决议

事件 • 决议