To begin any war in Imperator: Rome, you need a casus belli, that is the reason for the war. Any aggression must have some justification, otherwise you will not be able to fight with someone.
Not every nation can be targeted. You can only declare war on a nation in your diplomatic range. You can check this by turning on the political map mode. Countries highlighted in gray are out of your reach. You cannot trade with them or accept any diplomatic relations. Declaring war without casus belli is not recommended because you will lose stability points. For some, you will only get access under certain conditions and in certain situations.
Below is a list of possible reasons for war:
- Show superiority - Is a reason for war just to show the enemy your power and advantage over his army. The result of the war is awarded for the won battle, and when you have already collected 10 points, you will automatically receive more of them. This is a great solution when you see that the enemy is gaining strength and you have no other way to prevent it. The same reason is available in the "sea" version (show naval superiority). Here you need to win sea battles and block enemy ports.
- Conquest - you have the opportunity to conquer the province to which you already have claims. You have to conquer all the cities that belong to a certain province. This way it will not improve your score and you may start to receive points automatically. The longer the war lasts, the more the result of the war has the party that controls the specific province.
- Supporting rebels - this is an indirect reason for the war, because your state will automatically join the war, if an uprising breaks out in the targeted state. Your ally are rebels and you will fight with their previous government. On the other hand, any state in which we support the rebels will receive a casus belli on our government.
- Offer guarantee - you can offer care and protection to smaller nations if your state has regional power or even higher status. Any state that attacks a guaranteed nation will have to fight the state that provided the guarantees.
- Insult - we can insult other states by sending insult. Such a government receives a temporary casus belli and can declare war on us. It's a good decision if you don't have a reason for war and you don't want to lose stability points.
- Broken alliance/subject status - such reasons for war are possible only if the other state violates the terms of the treaty. In the case of the Alliance, these are important only in the situation when the other state will not respond to the call to war. If it renounces the treaty in peacetime through the diplomatic channel, you will not get "casus belli".
During every war you want to conquer the land, get money from the vault of the enemy, liberate the conquered state, or impose a vassal state to the enemy. Each of these actions is available when signing the sue for peace and depends on the results of the war. Casus belli also plays an important role here:
1) Warscore is carried out in several ways, such as victory in battle or the capture of the capital, but most often should be aligned with the "casus belli". If your reason for the war was the seizure of the province, you must occupy the entire area to start gaining points. If the enemy captures at least one city in this province, your progress in the war will disappear in favor of the enemy. Hostile states often do not accept the conditions of signing the peace pact if you have not reached the reason to war.
2) Any demand in the negotiations will also be noticed at the points of aggressive expansion. This is a negative factor that determines the militancy of your state. The higher, the more reluctant you will be to neighboring nations. If you take the lands that are not eligible, you will receive more points of AE, than in the case of claiming and obtaining rights to a selected province. It's similar with any other reason to war. Therefore, when planning a conquest, it is worth bearing in mind which reason you are going to choose and whether you have the opportunity to perform it during the war. Even if you want to conquer a large area of a hostile state, you should choose a province that will be easier and faster to conquer.
3) If you have achieved the objectives of your reason for war for a long time, you may receive information about the automatic signing of peace. If you do not sign the peace pact in the given time, it will be automatically turned on. It's worth to conquer some land and capture as many enemy cities as possible during this time. You often get extra slaves or money if you conquer enemy capitals.