The just war theory is a set of military principles based on philosophy, theology and even political policy. Adapted over the years by different Catholic philosophers and theologians, the just war theory has been fully embraced by the Catholic Church as acceptable means for military force. Most importantly, the just war theory serves as a guide to those having difficulty understanding war and morality.
Pointing to one person for the history of the just war theory is impossible, as many different Catholic philosophers and theologians have contributed to the theory over time. The theory came about based on moral concerns about going to war and was created to dictate behaviour during conflicts when they become morally necessary. The just war theory was intended as a directive to understand when it is morally permissible to go to war (just war) and when circumstances do not warrant war (unjust). Marcus Tillius Cicero, a Roman philosopher, and Saint Thomas Aquinas are both credited as early authors of the just war theory.
The just war theory is significant because it sets forth certain criteria by which the military must act during wars and conflicts. This theory has gained importance because it allows the average person to determine the just or unjust nature of a conflict. It has become increasingly important as the nature of war and combatants have evolved. When opposing combatants aren't part of a traditional military structure, it becomes difficult to apply certain aspects of the just war theory. As the face of war changes, it becomes especially important to update the just war theory.
The content of the just war theory is broken down into two parts: the right to go to war and the way in which soldiers conduct themselves within that war. Jus ad bellum, or the right to go to war, establishes that war may not be waged in order to recover stolen items or simply to punish those who have done wrong. Jus ad bellum dictates that war is only morally permissible when there is an imminent threat to innocent victims. Jus in bello is the portion of the just war theory that directs soldiers on how to act in combat. First, only enemy combatants should be the target of the war, not civilians. Next, the force used should not be worse than the act that prompted the war. Finally, the actions taken in combat must weigh the risks and rewards of the objective in order to limit the number of innocent civilian deaths.
The just war theory provides many benefits, especially to combatants against a larger and much wealthier opponent. The guidelines of just war require that war is only an option when all peaceful options have been completely exhausted, which would eliminate the possibility of a knee-jerk war. Furthermore, the theory takes steps to ensure that lives of innocent civilians that had nothing to do with the conflict are not at risk. The major benefit of the just war theory is how well it outlines acceptable behaviour during combat, with the main goal being to limit the loss of life for noncombatants.
Many alternative theories to the just war theory exist that seek to redefine war and its impact on societies. Militarism theory asserts that war isn't unjust but that it can be beneficial to society. Realism, on the other hand, says that morality has no place in international relations where a state should act in its own self-interest and security. Finally, pacifism finds all war morally wrong and finds no circumstances that would warrant war.