In Christianity the term was traditionally used by the Roman Catholic Church to refer to one who did not believe in the divinity of Jesus, knowingly held beliefs that contradicted Catholic dogma, or one who had not been baptized, or by Christians in general to describe non-Christians or those perceived as enemies of Christianity, including Muslims. Current English speaking Catholic ecclesiastical usage however distinguishes between non-Christians and non-believers (persons without religious affiliations or beliefs).
The Arabic word kafir (literally the one who "covers", in the sense of hiding) is the Muslim term for an infidel. The term technically applies only to atheists and polytheists and to those who subscribe to faiths other than Christianity, Judaism and Zorastrianisms. In common use, however, the term is also applied to Christians, especially in English fiction and poetry.
In recent years, Christian thought has avoided the use of the term infidel, especially in reference to Muslims and Jews. Current English speaking ecclesiastical usage however distinguishes between non-Christians and non-believers (persons without religious affiliations or beliefs). The current preference for these terms over the pejorative "infidel" also reflects the modern Roman Catholic Church's commitment to engage in dialog with persons of other, or no faith.
"Kafir" has also come to be regarded as offensive, thus Muslim scholars discourage its usage due to the Quran's command to use kind words. It is even a punishable offense to use this term against a Jew or a Christian, under Islamic law. Some Muslim extremists today however use the term in reference to all non-Muslims.
A long line of Papal hierocratic canonists, most notably those who adhered to Alanus Anglicus's influential arguments of the Crusading-era, denied Infidel dominium, and asserted Rome's universal jurisdictional authority over the earth, and the right to authorize pagan conquests solely on the basis of non-belief because of their rejection of the Christian god. In the extreme hierocractic canonical discourse of the mid-twelfth century such as that espoused by Bernard of Clairvaux, the mystic leader of the Cisertcians, legitimized German colonial expansion and practice of forceful Christianisation in the Slavic territories as a holy war against the Wends, arguing that infidels should be killed wherever they posed a menace to Christians. When Frederick the II unilaterally arrogated papal authority, he took on the mantle to "destroy convert, and subjugate all barbarian nations." A power in papal doctrine reserved for the pope. Hostiensis, a student of Innocent, in accord with Alanus, also asserted "... by law infidels should be subject to the faithful." and the heretical quasi-Donatist John Wyclif, regarded as the forefather of English Reformation, also held that valid dominium rested on a state of grace.
The Teutonic Knights were one of the by-products of this papal hierocratic and German discourse. After the Crusades in the Levant, they moved to crusading activities in the infidel Baltics. Their crusades against the Lithuanians and Poles however precipitated the Lithuanian Controversy, and the Council of Constance, following the condemnation of Wyclif, found Hostiensis's views no longer acceptable and ruled against the knights. Future Church doctrine was then firmly aligned with Innocents IV's position.
The rights bestowed by Romanus Pontifex and inter caetera have never fallen from use, serving as the basis for legal arguments over the centuries. The U.S. Supreme Court ruled in the 1823 case Johnson v. M'Intosh that as a result of European discovery and assumption of ultimate dominion, Native Americans had only a right to occupancy of native lands, not the right of title. This decision was upheld in the 1831 case Cherokee Nation v. Georgia, giving Georgia authority to extend state laws over Cherokees within the state, and famously describing Native American tribes as "domestic dependent nations." This decision was modified in Worcester v. Georgia, which stated that the U.S. federal government, and not individual states, had authority in Indian affairs, but it maintained the loss of right to title upon discovery by Europeans.
In recent years, Native American groups including the Taíno and Onondaga have called on the Vatican to revoke the bulls of 1452, 1453, and 1493.
In the Early Middle Ages, based on the idea of the superiority of Christians to infidels, regulations came into place such as those against forbidding Jews from possessing Christian slaves; the laws of the decretals further forbade Christians from entering the service of Jews, for Christian women to act as their nurses or midwives; forbidding Christians from employing Jewish physicians when ill; restricting Jews to definite quarters of the towns into which they were admitted and to wear a dress by which they might be recognized.
These rules have now given way to modern legislation and Catholics, in civil life, are no longer governed by ecclesiastical law.