The Baltic crusades acted as one element in a cruel process of Christianization and Germanization, providing a religious gloss to ethnic cleansing and territorial aggrandizement more blatant and, in places, more successful than anywhere else. Crusading in the Baltic, first applied to Danish and German anti-Slav aggression between the Elbe and Oder in 1147 during the Second Crusade, cloaked a missionary war which, given the Christian prohibition on forced conversion, represented a contradiction in canon law. These wars directly served local political and ecclesiastical ambitions. The main areas of conquest after 1200 included Prussia, Livonia, Estonia, and Finland. In Prussia, the expansion of land-grabbing German princes in Pomerania gave way to the competing interests of Denmark and the Military Order of Teutonic Knights. This order had originally been founded by Germans in Acre in the wake of the Third Crusade in the 1190s, but because of its regional associations soon became heavily, and ultimately almost exclusively, involved in fighting for the cross in the north. The fighting in Livonia devolved onto the church under the archbishop of Riga and the Military Order of Sword Brothers (founded in 1202). In Estonia the Danes again clashed with the Military Orders, as well as with Swedes and Russians from Novgorod. Finland became the target of Swedish expansion. By the 1230s, control of war and settlement in Prussia, Livonia, and southern Estonia had been taken up by the Teutonic Knights, with whom the Sword Brothers were amalgamated in 1237. In 1226 their Master, Hermann von Salza, was created Imperial prince of Prussia, which was declared a papal fief held by the Teutonic Knights in 1234. Although some specific grants for crusades in the Baltic continued, most of these northern wars adopted the character of ‘eternal crusades’ once Innocent IV in 1245 confirmed the right of the Teutonic Knights to grant crusade indulgences without special papal authorization. This gave the Teutonic Knights a unique status, not held even by the rulers of the kingdom of Jerusalem, of a sovereign government possessed of the automatic right of equating its foreign policy with the crusade. Cashing in on this in the fourteenth century, the Knights developed a sort of chivalric package tour for western nobles eager to see some fighting, enjoy lavish feasting, earn indulgences, and gild their reputations. The Knights’ appeal slackened with their failure to overcome Lithuania-Poland and the conversion of pagan Lithuania in 1386. Their transformation into a secular German principality was completed in 1525 when the Master of the Teutonic Knights in Prussia embraced Lutheranism and secularization. The Livonian branch followed suit in 1562.
On the face of it, the idea that the crusades in the Baltic were directed to conquer holy lands appears fanciful, given that the regions attacked had no Christian pre-history. Yet perhaps precisely because of its extreme incongruity, this concept gained credence: alone of the regimes established in the wake of crusader conquest, Prussia and Livonia were ecclesiastical states. The association came early. A propagandist exhortation to attack the Wends east of the Elbe in 1108 described the campaign as being to liberate ‘our Jerusalem’. This challenging analogy operated in ways that remained central to the early association of crusading with German expansion eastwards; cashing in on the new impetus to holy war provided by the Jerusalem wars; the need to defend Christendom; and the implication that the wars were aimed at recovering lost Christian land. Some lands beyond the Elbe targeted by German crusaders in the twelfth century had been occupied by the Ottonian emperors before the great Slav revolt of 983 drove them back. Other areas had experienced more recent missionizing of fluctuating success. On the shifting German-Slav frontier, areas that had been conquered, even as far back as the tenth century, and then lost could attract accusations of apostasy. This confusion could work the other way; one contingent of the 1147 crusaders found themselves besieging recently Christianized Stettin.
The distinctive character of the Baltic crusades lay in the explicit alliance of crusade and conversion, or, as saintly Bernard of Clairvaux put it, conversion or extermination. Innocent III freely employed the language of compulsion to ‘drag the barbarians into the net of orthodoxy’. This unsound doctrine acknowledged the religious component in ethnicity, cultural identity, and racial awareness. In contrast with Spain or the Near East, in the Baltic, conversion came as the inevitable corollary and recognition of conquest. Paradoxically, this allowed for greater cultural accommodation and transmission from Slav to German and vice versa. Descendants of the pagan Wendish prince Niklot, victim of the first crusader attack in 1147 and killed by Christians in 1160, became the Germanized princes and dukes of Mecklenberg, one of whom joined a crusade to Livonia in 1218. However repellent to the religiously fastidious, enforced conversion worked; by 1400 the Baltic had become a Latin Christian lake, even if elements of pagan culture swam freely beneath the surface. Conversion not backed by coercion would have had a harder struggle, as the successful resistance of pagan Lithuania showed, only accepting conversion undefeated on its own terms in 1386. The application of crusading incentives from the mid-twelfth century did not manufacture this link between force and faith, it merely recognized a process of cultural and political Imperialism already well established.
Crusading in the Baltic contributed to the twelfth-century German expansion into territory between the Elbe and Oder and western Pomerania; thirteenth-century German penetration into the southern Baltic lands between the Vistula and Niemen, Prussia, Courland, and later, in the fourteenth century, Pomerelia west of the Vistula; the transmarine colonization of Livonia by a combination of churchmen and merchants from German trading centres such as Lübeck and Bremen; the aggressive expansionism of the Danish crown, especially in northern Estonia; and the advance of the Swedes into Finland. Until the thirteenth century crusading, as opposed to more general associations of war with Divine favour, played only an intermittent role. The application of crusade privileges to the summer raids on the western Wends during the Second Crusade in 1147 had more to do with buying Saxon support and internal peace within the empire in Conrad III’s absence in the Holy Land than the institution of a new sustained crusade front. One of the protagonists in the 1147 expeditions, Albert the Bear, did not need crusade privileges to carve out a principality of Brandenberg beyond the Elbe; his territorial acquisitiveness was in any case portrayed by apologists as attracting God’s approval. Such conquests went together with the implanting of bishoprics and monasteries and so earned clerical plaudits. The secular reality was brutal for the conquered, harsh for the German and Flemish settlers, and, as one pious frontier priest lamented, encouraged the avarice rather than the piety of another 1147 crusader, Henry the Lion, duke of Saxony. Between 1147 and 1193 only one papal crusade grant was directed towards the Baltic, in 1171. However, the often savage wars of conquest and conversion conducted against the Slavs by the German princes and kings of Denmark were recognized by the papacy as ‘inspired with the heavenly flame, strengthened by the arms of Christ, armed with the shield of faith and protected by divine favour’, as Alexander III put it in 1169. Nonetheless, to ascribe responsibility for medieval German Imperialism on the crusade would be misleading; one might as well accuse the Christian Church. It might also be added that the Baltic pagans were no less keen on massacring opponents and eradicating symbols of an alien faith. Although, except in Lithuania, the pagan holy wars ended in defeat this does not mean they did not happen.