Huge Disclaimer – I am not a scholar of Just War theory, nor one of medieval philosophy and warfare. This is information I compiled in order to teach a lesson on the Baltic Crusades.
In 1147, March saw a gathering of the nobles of the Holy Roman Empire in Frankfurt. This was both for the Easter feast, and because the Pope had sent a messenger calling the nobles to a second crusade in the holy land. The nobles were attentive, but not overly enthusiastic for the long journey to the Holy Land. Instead, several of them proposed a closer, but equally urgent, cause. The pagans along the Baltic Shore had threatened Christians in the past, and on at least three occasions had shaken off their conversion, lapsed to paganism, and gone to war. Could His Holiness extend the protections and dispensations granted to those defending Jerusalem from the Seljuks to those defending Christians in the north, and spreading Christianity there? In June, Pope Eugene III agreed, and the Baltic Crusades began.
The case for the First Crusade had been quite clear. Christian pilgrims and Christians still living in Palestine were being enslaved, murdered, robbed, and harassed by the Seljuk Turks, who also threatened the Byzantine Empire. In 1050 going to war to liberate Jerusalem after 400 years of Moslem rule seemed quite reasonable. After all, were Christians not also fighting in Iberia to drive out the Moorish invaders? And fighting in self-defense was most certainly permitted by the Church. Thus the First Crusade was “right” and a proper sort of war, even if the conduct of all sides did not always live up to what was desired.
The Baltic Crusade, however, seems different. Granted, not long after the Crusade was declared but before any Christians had attacked anyone, the pagan Prince Niklod of the Slavic Abodrite tribe attacked Lübeck and the surrounding areas, looting, carrying off captives, sinking merchant ships, and then retreating to a stronghold to sit out a rather ineffective siege later that fall. So Prince Niklod had managed to make it a defensive war of sorts, at least at first.
The idea of “missionary war” seems very strange to modern Christian thinking. At the time, very few people questioned the idea. It went back to Augustine of Hippo’s teachings in the early 400s—derived from writings by St. Ambrose of Milan, according to some scholars—about the flawed nature of the world and that fighting was not always inherently bad. Martin of Tours, writing not quite a century later, made a similar point, expanding it somewhat to include protecting those who had expressed a desire to convert, although he was opposed to killing heretics and pagans simply for being heretics or pagans. The Franks, going back to Clovis in the 500s, had a habit of fighting heretics (aka Arian Christians) as well as preemptive fighting to prepare the way for missionaries in addition to defending and avenging missionaries. And lapsed pagans, those who renounced their baptism and resumed war against Christians, were seen as being in need of punishment and re-conversion.
Keep in mind that faith and fealty were intertwined. To accept Western Christianity meant accepting, at least nominally, the overlordship of the Holy Roman Empire. The First Crusade’s call had included the idea of “dilitatio Christi,” or spreading Christendom, that is the lands of [Western] Christianity. North of the Alps, that generally included the hegemony of the Holy Roman Emperor and other monarchs supported by the papacy. “A ministry of sword and shield” was not seen as anything wrong, so long as the Christians upheld the standards set by the Church and any limits and rules established by the Holy Roman Empire.
What guided the methods of warfare? The Old Testament, as well as the New. There are many examples of the Lord commanding the Children of Israel to wage war against certain groups, or to continue war against certain groups, and also instructions on what was permissible and what was not. Deuteronomy 20 contains set rules on warfare, and was used as the foundation for proper behavior. It was not always followed, and by later standards it was considered rather barbaric. But in 1050, 1147, and on through the 1400s, it was better than nothing, especially if tempered by the teachings of the Gospels. And several popes renewed the permission to use war in service of the faith on at least two occasions, as well as encouraging military brotherhoods such as the Livonian Brothers and the Teutonic Knights.
To modern ears it jars to read of Mary, Queen of Heaven and of Victory, being praised with the words, “See how many kings… and elders of treacherous pagans She has wiped off the earth.” To medieval ears it was perfectly fitting.
The ideas about missionary warfare and spreading Christendom by the sword began to wane in the 1300s, as the church sought to put stricter limits on both the causes and the conditions of war among Christians. St. Thomas Aquinas, in his magisterial Summa Theologica, presented three qualifications for a just war, one that could be waged without incurring the wrath of the Church (although it was best to avoid war, and individual misconduct still required penance): War is the last resort, it is only waged by legitimate authority, in response to a wrong suffered by a legitimate party. Self defense is always just BUT it should only be waged to bring justice, not to take a life in exchange for an eye, so to speak.
Once war has been decided upon, it must have a good chance of being won, it must be proportional, care must be taken to avoid the innocent and to prevent excessive damage. This was later expanded into what we think of as the laws of war, the Hague and Geneva Conventions, and other things. But for this essay, we will stop with Aquinas. The link in the Summa takes you to his requirements.
During the Council of Constance in 1415, a professor from the Jagiellonian University in Poland and a representative from the Teutonic Knights went before the church council to determine if the Teutonic Knights had a right to take land from the Poles and Lithuanians, now that the Poles and Lithuanians had officially converted to Christianity and were ruled by the same family. However, the Poles went farther, asking if the wars in the Baltic were still justified as Just Wars and crusades. They were no longer strictly defensive (not that they had always been defensive, just part of the time), they were being waged against fellow Christians, there was no-longer such a clear-cut provocation, and the proportionality of the fighting was not quite what Aquinas had envisioned.
The idea of a semi-preemptive “missionary war” was no longer popular with Church leaders. Conversion by persuasion and example was now considered to be better than mass baptism following military defeat as had been practiced from the time of Constantine through 1400. Especially since Poland was now Catholic. Even if there were some pagans still in the swamps and woodlands, the Teutonic Order was not a legitimate authority when compared to the Crown of Poland. And carrying off the property and women and children of the defeated pagans, while approved in Deuteronomy 20, was not approved any longer as a proper means of conducting war. The Teutonic Order would last as a political unit until 1525, and still exists today as a service organization, but the days of the Baltic Crusade’s church-sanctioned warfare were passing rapidly.
I suspect, although I am venturing well outside my limited knowledge base, that the growing strength of secular institutions such as the French and English monarchies, the Holy Roman Empire, the crown of Poland, and the advance of the Reconquista in Spain also had an effect on shifting what could be considered Just War. The smaller nobles and barons now had stronger overlords who could check them more easily, and the Church depended on the greater monarchs for support against threats like the Ottomans. There wasn’t room for regal states like Poland and events like the Baltic Crusades both in the same area of Christendom. And the strength of the regal states was growing when compared to that of the pagans and the regional lords. Granted within the Holy Roman Empire things were a little different, but the Empire had developed institutions to help keep the peace within its borders, and something like the stricter standards of Aquinas’s Just War Doctrine strengthened the Empire and other regal states.
Times had changed. Just War required tighter justifications with more stringent limits on proper behavior once war had been declared. The medieval world was sliding toward the early modern, although not without a few relapses, most notably the Thirty Years War.
Sources: Burnam W. Reynolds. The Prehistory of the Crusades: Missionary War and the Baltic Crusades (Bloomsbury Academic Press, NY, 2016) is an excellent source with long discussions of the changing definitions of just war as they apply to crusades and especially the Baltic. Highly recommend. Available in print and electronic versions.
Artis Aboltins and Santa Jansone “Bishops in Livonia” Medieval Warfare Vol. VI, No. 3 (2016) is an interesting article about the fighting bishops of the Baltic, several of whom died in battle.
The above site is a compendium of material about Just War Theory both classical and modern. It is not that well organized, but has lots and lots of links.
The applicable section of the Summa is linked in the text above.
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