U.S. Marines direct a concentration of fire at the enemy, Vietnam, 8 May 1968
Issue indivisibility occurs when the two parties cannot avoid war by bargaining because the thing over which they are fighting cannot be shared between them, only owned entirely by one side or the other. Religious issues, such as control over the Temple Mount in Jerusalem, are more likely to be indivisible than economic issues.
A bigger branch of the theory, advanced by scholars of international relations such as Geoffrey Blainey, is that both sides decide to go to war and one side may have miscalculated.
Some go further and say that there is a problem of information asymmetry with incentives to misrepresent. The two countries may not agree on who would win a war between them, or whether victory would be overwhelming or merely eked out, because each side has military secrets about its own capabilities. They will not avoid the bargaining failure by sharing their secrets, since they cannot trust each other not to lie and exaggerate their strength to extract more concessions. For example, Sweden made efforts to deceive Nazi Germany that it would resist an attack fiercely, partly by playing on the myth of Aryan superiority and by making sure that Hermann Göring only saw elite troops in action, often dressed up as regular soldiers, when he came to visit.
The American decision to enter the Vietnam War was made with the full knowledge that the communist forces would resist them, but did not believe that the guerrillas had the capability to long oppose American forces.
Thirdly, bargaining may fail due to the states' inability to make credible commitments.[130] In this scenario, the two countries might be able to come to a bargain that would avert war if they could stick to it, but the benefits of the bargain will make one side more powerful and lead it to demand even more in the future, so that the weaker side has an incentive to make a stand now.
Rationalist explanations of war can be critiqued on a number of grounds. The assumptions of cost-benefit calculations become dubious in the most extreme genocidal cases of World War II, where the only bargain offered in some cases was infinitely bad. Rationalist theories typically assume that the state acts as a unitary individual, doing what is best for the state as a whole; this is problematic when, for example, the country's leader is beholden to a very small number of people, as in a personalistic dictatorship. Rationalist theory also assumes that the actors are rational, able to accurately assess their likelihood of success or failure, but the proponents of the psychological theories above would disagree.
Rationalist theories are usually explicated with game theory, for example, the Peace War Game, not a wargame as such, rather a simulation of economic decisions underlying war.
[edit]Political science

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The statistical analysis of war was pioneered by Lewis Fry Richardson following World War I. More recent databases of wars and armed conflict have been assembled by the Correlates of War Project, Peter Brecke and the Uppsala Conflict Data Program.
There are several different international relations theory schools. Supporters of realism in international relations argue that the motivation of states is the quest for security. Which sometimes is argued to contradict the realist view, that there is much empirical evidence to support the claim that states that are democracies do not go to war with each other, an idea that has come to be known as the democratic peace theory. Other factors included are difference in moral and religious beliefs, economical and trade disagreements, declaring independence, and others.
Another major theory relating to power in international relations and machtpolitik is the Power Transition theory, which distributes the world into a hierarchy and explains major wars as part of a cycle of hegemons being destabilized by a great power which does not support the hegemons' control.
Military adventurism can sometimes be used by political leaders as a means of boosting their domestic popularity, as has been recorded in US war-time presidential popularity surveys taken during the presidencies of several recent US leaders.[131]
[edit]War ethics

Morning after the Battle of Waterloo, by John Heaviside Clark, 1816

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The seeming contradiction between warfare and morality has led to serious moral questions, which have been the subject of debate for thousands of years.[132] The debate, generally speaking, has two main viewpoints: Pacifists, who believe that war is inherently immoral and therefore is never justified regardless of circumstances, and those who believe that war is sometimes necessary and can be moral.
There are two different aspects to ethics in war, according to the most prominent and influential thought on justice and war: The Just War Theory.[133][134] First is Jus ad bellum (literally translated as "right to war"), which dictates which unfriendly acts and circumstances justify a proper authority in declaring war on another nation. There are six main criteria for the declaration of a just war: first, any just war must be declared by a lawful authority; second, it must be a just and righteous cause, with sufficient gravity to merit large-scale violence; third, the just belligerent must have rightful intentions – namely, that they seek to advance good and curtail evil; fourth, a just belligerent must have a reasonable chance of success; fifth, the war must be a last resort; and sixth, the ends being sought must be proportional to means being used.[135][136]
Once a just war has been declared, the second standard, or aspect, is put into effect. Jus in bello, which literally translates to "right in war", are the ethical rules of conduct when conducting war. The two main principles in jus in bello are proportionality and discrimination. Proportionality regards how much force is necessary and morally appropriate to the ends being sought and the injustice suffered.[137] The principle of Discrimination determines who are the legitimate targets in a war, and specifically makes a separation between combatants, who it is permissible to kill, and non-combatants, who it is not.[137] Failure to follow these rules can result in the loss of legitimacy for the just war belligerent, and so thereby forfeit the moral right and justice of their cause.[134]

In besieged Leningrad. "Hitler ordered that Moscow and Leningrad were to be razed to the ground; their inhabitants were to be annihilated or driven out by starvation. These intentions were part of the 'General Plan East'." – The Oxford Companion to World War II.[138]
The Just War standard is as old as Western Civilization itself, and still has significant impact on thinking about the morality of wars and violence today.[139] Just War Theory was foundational in the creation of the United Nations and in International Law's regulations on legitimate war.[132]
These two positions generally cover the broad philosophical and ethical bents mainstream society. However, there are several theories on and about War which are in the minority in culture, but which, because of the influence they have had in recent history, demand mention here. These strains of thought on human society and war can be broken up into two main camps: Marxist and Fascist, both of which view war as purely practical.
Marxism, and other such historicist ideals, hold that history advances through a set of dialectics (as stated by Heinrich Moritz Chalybäus: thesis, antithesis, synthesis). Marx, and his followers, in particular held that history advances through violence. Marxism–Leninism, in fact, held the belief that outright incitement to violence and war was necessary to topple Capitalism and free the proletariat. In these theories, the question of ethics has no place, as the value of the war is entirely dependent on whether it advances the revolution or synthesis.
Fascism, and the ideals it encompasses, such as Pragmatism, Racism, and Social Darwinism, hold that violence is good.[140][141] Pragmatism holds that war and violence can be good if it serves the ends of the people, without regard for universal morality. Racism holds that violence is good so that a master race can be established, or to purge an inferior race from the earth, or both. Social Darwinism thinks that violence is sometimes necessary to weed the unfit from society so that civilization can flourish. These are broad archetypes for the general position that the ends justify the means.
[edit]See also