Just war theory in the context of "St. Augustine"

Augustine of Hippo (/ɔːˈɡʌstɪn/ aw-GUST-in, US also /ˈɔːɡəstiːn/ AW-gə-steen; Latin: Aurelius Augustinus Hipponensis; 13 November 354 – 28 August 430) was a theologian and philosopher, the bishop of Hippo Regius from Thagaste in Numidia Cirtensis, (present-day Souk Ahras, Algeria). His writings deeply influenced the development of Western philosophy and Western Christianity, and he is viewed as one of the most important Church Fathers of the Latin Church in the Patristic Period. His many important works include The City of God, On Christian Doctrine, and Confessions.

According to his contemporary, Jerome of Stridon, Augustine "established anew the ancient Faith". In his youth he was drawn to the Manichaean faith, and later to the Hellenistic philosophy of Neoplatonism. After his conversion to Christianity and baptism in 386, Augustine developed his own approach to philosophy and theology, accommodating a variety of methods and perspectives. Believing the grace of Christ was indispensable to human freedom, he helped formulate the doctrine of original sin and made significant contributions to the development of just war theory. When the Western Roman Empire began to disintegrate, Augustine imagined the Church as a spiritual City of God, distinct from the material Earthly City. The segment of the Church that adhered to the concept of the Trinity as defined by the Council of Nicaea and the Council of Constantinople closely identified with Augustine's On the Trinity.

The Crusading movement was a major religious, political and military endeavour of the Middle Ages—began in 1095 when Pope Urban II, at the Council of Clermont, proclaimed the First Crusade to liberate Eastern Christians from Muslim rule. He framed it as a form of penitential pilgrimage, offering spiritual rewards. By then, papal authority in Western Christendom had grown through church reforms, and tensions with secular rulers encouraged the notion of holy war—combining classical just war theory, biblical precedents, and Augustine's teachings on legitimate violence. Armed pilgrimage aligned with the era's Christocentric and militant Catholicism, sparking widespread enthusiasm. Western expansion was further enabled by economic growth, the decline of older Mediterranean powers, and Muslim disunity. These factors allowed crusaders to seize territory and found four Crusader states. Their defence inspired successive Crusades, and the papacy extended spiritual privileges to campaigns against other targets—Muslims in Iberia, pagans in the Baltic, and other opponents of papal authority.

The Crusades fostered distinctive institutions and ideologies, having a great impact on medieval Europe and the Mediterranean. Though aimed primarily at the warrior elite through appeals to chivalric ideals, they depended on broad support from clergy, townspeople, and peasants. Women, despite being discouraged, were involved as participants, proxies for absent crusaders, or victims. Although many crusaders were motivated by indulgences (remission of sins), material gain also played a part. Crusades were typically initiated through papal bulls, with participants pledging to join by "taking the cross"—sewing a cross onto their garments. Failure to fulfil vows could result in excommunication. Periodic waves of zeal produced unsanctioned "popular crusades".

The law of war is the part of international law that regulates the conditions for initiating war (jus ad bellum) and the conduct of hostilities (jus in bello). Laws of war define sovereignty and nationhood, states and territories, occupation, and other critical terms of law. Among other issues, the modern laws of war address the declarations of war; acceptance of surrender and the treatment of prisoners of war; the principles of distinction, as well as military necessity and proportionality; and the prohibition of certain weapons that cause unnecessary or excessive suffering.

The law of war is considered distinct from other bodies of law—such as the domestic law of a particular belligerent to a conflict—which may provide additional legal limits to the conduct or justification of war. The term law of war, or jus in bello, overlaps to some degree with opinio juris (also referred to as customary law), but refers to a very specific body of international law composed of customary and treaty-based law.

A war of aggression, sometimes also war of conquest, is a military conflict waged without the justification of self-defense, usually for territorial gain and subjugation, in contrast with the concept of a just war.

Wars without international legality (i.e. not out of self-defense nor sanctioned by the United Nations Security Council) can be considered wars of aggression. However, this alone usually does not constitute the definition of a war of aggression: certain wars may be unlawful but not aggressive (a war to settle a boundary dispute where the initiator has a reasonable claim, and limited aims, is one example).

Jus post bellum (/juːs/ YOOS; Latin for "Justice after war") is a concept that deals with the morality of the termination phase of war, including the responsibility to rebuild. The idea has some historical pedigree as a concept in just war theory. In modern times, it has been developed by a number of just war theorists and international lawyers. However, the concept means different things to the contributors in each field. For lawyers, the concept is much less clearly defined, and many have rejected the usefulness of the concept altogether. The concept continues to attract scholarly interest in the field of international humanitarian law. A famous example of Jus post bellum is the reconstruction of Germany by the Allies post World War 2.