Few people on this planet are happy about the war. Is that people who benefit from it and who use the war to satisfy their political, and most often economic interests. But what to do if the war is brewing due to some far-fetched reasons, and no one wants to fight. Well, or almost no one.
We need to use pacifist organizations. Demonstrations, expressions of protest, “Die-in” actions - this is an incomplete list of actions that can be used by pacifists in the fight against imperialism and militarism.
Pacifists attract the attention of the authorities and citizens, trying to educate those around them that wars are unnecessary to resolve interstate disputes. The authorities, of course, often ignore them, but if the pacifists manage to raise the population against the war, then the aggressor state will simply have no one to fight with and probably it can curtail its aggressive intentions.
Using a nuclear shield - reduces the threat of world war. If things have gone so far that war between countries could not have been avoided, and pacifist organizations work worse than state propaganda, then there is a very reliable way to deter the enemy - a nuclear shield.
Currently, 9 countries officially or presumably own nuclear weapons. Among them are the old nuclear powers that have signed the nuclear non-proliferation treaty - Russia, the United States, France, Great Britain, China. There are also a number of countries that have not signed this agreement - Israel, India, Pakistan and North Korea.
A war between all these countries is difficult, since a possible aggression on the one hand will be followed by an adequate response on the other.
Use territorial or economic concessions to appease the aggressor. Of course, this is the very last thing when war cannot be avoided. If the head of the country sees that his troops are obviously weaker, he can use this humiliating step, for many, namely, give the aggressor what may be the cause of the war. As a rule, this can be some kind of territory or the aggressor's access to resources.
Few people would take such a step, especially in history there were precedents of appeasing an aggressor, which eventually ended in World War II.