Basis of warfare

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War strategy is very different if against the AI or other human players, as usual. If you want to play MP, there are two excellent guides for MP warfare on the forum, Ryoken's tactical dominbation guide and Damo and Dukey's guide to warfare and diplomacy. Against the AI you only need a war strategy if you are weaker, poorer and smaller than the AI alliance. But a strategy will also minimize your loses.

Warscore

The way the warscore is computed emphasizes capturing provinces over fighting battles. Furthermore, the AI is not efficient in its own war strategy: it tends to select a single province and send all force to that province to siege. It follows that the best strategy is to lead the siege of as many enemy provinces as possible, from as early as possible (be ready if you are DoW) and using all your tools to conquer them as soon as possible (siege bonuses, naval blockade, artillery). As long as you manage to carry on two or three sieges for every enemy siege on your side, you will win the war. Battles have a much lower impact and are very expensive, so you should avoid them unless you find low morale armies (fresh recruits or retreating foes) or tiny ones that can be used to raise the warscore. A small retreating army inside your territory is good for continuous abuse or even ping-pong beating. Avoid pitched battles of uncertain result even if it means abandoning a siege, or the next war will caught you with insufficient armies. If you are caught unprepared by the DoW, to win the war you will have to reject unfavorable peace offers until the warscore turns in your favor. If you are going to lose, buy peace before your provinces fall. See if you can increase your warscore and sign a white peace.

Strategies

The AI is blind to topography and will gladly attack with cavalry in the mountains, and attack across a strait or river with inferior forces. I cannot predict how the AI will react to my armies, sometimes it ignores them, sometimes it avoids them, and sometimes it attacks them. In general it appears that at the start of the war, every country in the enemy alliance choses a province (two at most) and moves part or all of his forces to besiege it. If your armies happen to be in the way, battles will ensue. I think the province is chosen by its value and desirability (core, etc.) and usually is the same for most or all the alliance members, so they all pile their armies on that province. Freshly recruited armies are sent to that province regardless of the size of the besieging army already there, until the province is taken by whoever happens to be the siege leader. Then they all chose a new province and move their armies. The AI is absolutely ignorant of attrition, winter and supply lines. It seems to know about blockades and definitely knows when you have sieges on his provinces, although he may not do anything about it. Often times the AI makes the worst tactical decisions, like splitting the forces when there are strong enemy forces nearby. On top of all this, the AI doesn't know if it is winning or losing the war. It may declare war and come in full force only to ask for a ridiculous amount of money when you think you are going to be swallowed. Given all the shortcomings, the AI is not a difficult enemy and this makes possible to win the game with a small, poor country, that in real history disappeared 400 years ago.

Winter war

Winter in EU2 goes from November 1st to March 30th. During this time most Northern provinces, and some more meridional will be covered by snow, turning white colored. In the meridional provinces, snow is random both in location and duration. As we have seen snow will have a reduction of supply limit by -25 if you don't own the province, and will increase the maximum attrition, making this provinces very effective lethal traps.

Winter war is therefore a special kind of war where your main enemy is by far attrition. It requires a special strategy to reduce loses. It takes place in provinces that are covered in snow some time of the year, every year. The general idea is that you avoid fighting during the winter months and try to limit foreign soil operations to march-november period. Most northern european provinces in Scandinavia and Russia will have zero supply limit and huge maximum attrition during winter. Ideally you prepare in advance for it and declare war on February. You should know the time it will take your troops to arrive, so they enter the province after the 1st of March but as close to it as possible. If snow is still present in March you cancel movement or retreat so you are out by the 30th of March and come back to arrive in April. Summer operations are as usual, but you do not go deeper into enemy territory unless you can take provinces in a few months (usually with a high siege bonus leader and cannons). On November, if snow comes you retreat to your provinces. If the siege is progressing well you will want to leave a cover force of over 1000 men per fortification level. To avoid the siege from failing, you will, at the same time, send a small infantry force (say, 500-1000 men) from your reserve force to reinforce the siege. They will provide the inevitable popsicles for a couple of months, when you will have to send more. Ideally you will have several sieges going at the same time. If the enemy comes in force to lift one, don't hesitate to abandon it. Even if you send your army and win, your loses will multiply with attrition during combat. If the enemy comes to your territory, avoid them and let general winter do the fighting. The AI unfortunately doesn't know how to fight in winter, so their attrition loses will be awful. Let them siege. Once you control one level of depth into enemy territory you have two choices: collect your reward at the peace table or go one level deeper. The small increase in supply limit from controlling the province won't help you during winter, so you will take inevitably a lot more attrition, so you have to know if your manpower, recruiting capacity and economy can deal with it.

Some more advice: leaders with a siege bonus help a lot by speeding sieges, but leaders with a high movement rate will reduce attrition so they are even more useful. Keep those in the cover force during winter through army management, provided you can keep them alive with reinforcements when necessary. Leave leaders with movement rate of 1 at home, they have a limited use in winter war. Naval blockade is very much needed if you have naval superiority, otherwise port provinces will be very difficult to take. Do not keep your troops in the ships during the winter, they will also suffer from high attrition. If you have military access with your enemy, it will help you a lot by doubling your supply limit. You will then have to wait for them to DoW you, or DoW any of their allies and hope they don't dishonor.

One tactic of winter war not discussed so far is that of "bouncing" siege armies. A siege progresses so long as the amount of troops is 5K times the fortress level. The troops can be present (and not in motion) at any time during the month to get the cannon symbol on the siege. Once the cannon is present, only a cover force need remain until the cannon ultimately fires 30 days later. Then, the high number of troops must be present in the province once more to reestablish the cannon symbol. Cavalry are especially good at bouncing in and out of provinces, since cavalry can typically move two provinces in the same 30 day period. Infantry will work as well, but movement attrition is required. Bouncing armies are good any time there is a siege in low supply areas. Bouncing armies can often keep two sieges progressing in two provinces simultaneously.

Peace negotiations

At the conclusion of war, a Peace Treaty is necessary to restore peaceful operations. To gain a 100% warscore requires gaining control of all of an enemy’s city provinces; otherwise, the maximum warscore is 99%. By gaining a 100% warscore you can sometimes force peace on any terms you propose, not exceeding 100% in warscore. However, the AI is usually reluctant to make peace at 100% if the AI has any military at all. Even one ship or conquistador halfway around the world or a tiny band of infantry, where the AI has military access and you do not, is enough to prevent you from claiming all you truly deserve. You may try peace offers of 99%, 89%, 79%, 74%, 69%, 59%, and/or 49%. Peace at 49% warscore is always accepted if you have 100% warscore. Warmongering countries like France and Russia, as shown in the country's AI file under ferocity, are less likely to accept your peace offer.

Offers at 49% are usually acceptable when 70% warscore is obtained; so if that's all you are aiming for, think twice about completing all the sieges needed for more warscore with warmongering countries. It is not necessary to control an enemy's trade posts or sub-city colonies for 100% warscore; however if you do not control everything, you run into the same problems with peace proposals as if the AI had some military remaining.

Above 49%, demands that AI give up both money and one or more core province are less likely to be accepted; if the AI is being reluctant don't bother demanding that small amounts of cash be thrown into deals above 49%. The more warscore worth of core provinces you demand, the less likely the AI is to accept; try balancing demands with colonies or other provinces that are not cores for the AI. Consider AI core provinces as worth twice as much as is stated in the demand within the game. Depending on how many diplomats you have and are receiving and depending on how desperate you are for peace will determine how much haggling you are willing to do.

It is rumored that, the AI is more likely to accept peace when a player controls the AI’s capital. Also, having a current siege against the AI may help. Making separate peace with the AI leader’s allies may help. Reducing the strength of the AI’s army may help.

Be careful not to allow other nations to claim sieges in small, low taxable countries. You can control four out of five provinces but that does not mean 80% warscore. The warscore contribution of a province depends on base tax, fortress level, presence of manufactory, core status, and CoT status. So for example, you could control four provinces for only 24% war score. Even if one of your allies grabs the fifth province, you are not going to have much bargaining power.

Controlling your enemy's capital province and obtaining a 70% warscore allows you to demand that they become your vassal (if they are not already vassals of someone else). Regardless of whether or not the enemy's capital is controlled, obtaining a 50% warscore allows you to demand that your enemy convert to your religion (if they are eligible to do so). Force conversion is only permitted in an offer that is a separate peace for the enemy; see below.

A 20% warscore can be used to demand military access, which allows your troops and ships to be based in their territories in peacetime. Various amounts of warscore may be used to demand that they permanently turn over provinces to you or your allies; note that only provinces owned by the negotiating country on the losing side may be transferred, not provinces owned by its allies.

By clicking on the coats of arms in the Peace Treaty screen, you may choose to negotiate on behalf of only yourself or your entire alliance (only if you are the leader) and if your enemy is agreeing on behalf of themselves or their alliance (again, only if they are the leader). Religious conversions cannot be proposed if the losing country is negotiating for its whole alliance (even if it, in fact, has no allies).

Provinces can only be demanded if they are a core province of, or controlled by, a country in the winning alliance. Uncontrolled core provinces cost double the amount of warscore as they would if they were controlled. Demanding an uncontrolled core province requires the owner to currently control the province.

If you are winning a war against a country with only one province, or Pagan religion, you may demand that their entire country become part of your own. Non-Pagan countries with more than one province cannot be conquered in this way; you must either forcevassal them or reduce their number of provinces.

Unless a long time is spent at war, demands for white peace (i.e. no tribute) are less likely to succeed than demands for reparations. The AI has been biased toward not accepting white peace, although they may gladly hand over or accept spoils that benefit them by 11% of current warscore. The AI must have 50d in their treasury before you can demand money only. Similarly, the least amount you can offer in money alone is 50d.

If the AI does not give in to your demands, you may have to accept one of the AI’s peace proposals. The good news is, you can get 99% in spoils from 99% victory in this manner. The bad news is, the AI generally offers a relatively large number of the least desirable provinces and full treasury that nearly adds up to your warscore advantage. An exception is that the AI usually gives up a valuable CoT when the warscore advantage is very large.

When selecting provinces for offer, the AI’s first priority is giving up provinces that are not cores for the AI: trade posts, sub-city colonies, and other cities, in that order. Except for CoTs in case of large warscore, the lower the warscore contribution of a province, the more likely it is to be offered. Generally this means the lowest base tax provinces with lowest fortresses and no manufactories are offered first. Next, the AI offers its least valuable cores.

All provinces that the AI will offer are always either core provinces for you, or are provinces that you control and either border one of your provinces or border a body of water. If you know you are relying on the AI’s peace proposal at the outset of the war, do not take control of low base tax provinces that you do not want offered to you; you can cover low tax provinces and gain warscore by winning battles against small units of new recruits at 1% for each battle.

If you are planning to be in multiple wars and the AI does not have many provinces that border you or the sea, or those provinces are not ones that you want, you may like to fall back on demanding 49% peace in a first war to gain provinces that border other provinces that you would like to have offered to you in future wars. Remember, you need to be able to defend new provinces from rebellion, so military access from some nation may be required. If you demand military access as part of the 49% peace, then you need a way to get another war without losing military access such as badboy war or warring with one of their allies.

When the AI makes a peace offer, the AI usually attempts to avoid having isolated provinces. However, you can cause the AI to offer provinces that result in isolation by picking and choosing first which provinces you border and then which provinces you control. Causing isolation can be a way to gain provinces by defection. It is more difficult for the AI to defend an isolated province.

Automatic peace

In some cases, a war can end in a Peace Treaty being imposed by the game, without peace negotiations taking place. This can happen in two circumstances:

- A "White Peace", meaning no concessions are given to either side, occurs whenever there has been no combat and no occupations for a period of 3 years.

- Turboannexation

Other warfare related concepts