The Northern Crusades, otherwise known as the Baltic Crusades, were religious wars that took place in the 12th and 13th centuries in order to subjugate and forcibly baptize the indigenous peoples of various parts of Northern Europe such as Finland and North and Eastern Germany, but most significantly the areas of modern day Estonia, Latvia and Lithuania. The official starting point for the Northern Crusades as a whole was Pope Celestine III’s call in 1195, but the Christian kingdoms of Denmark, Sweden, Poland, and the Holy Roman Empire had already begun to subjugate their pagan neighbours before then.
The part of these Northern Crusades that seems to have been the main focus of the action, and continued in some form or another for almost 100 years was the Livonian Crusade which took place across what is now the Baltic states of Estonia and Latvia. This crusade takes it’s name from the Livonians, who were the indigenous inhabitants of modern Northern Latvia and Southwestern Estonia, usually referred to as Livonia. Other than the Livonians, during this period the other groups in the region that were a target of this crusade were the Latgalians, Selonians, Estonians, Curonians, and Semigallians.
These peoples inhabiting the Eastern shores of the Baltic were, by the time of the first crusading in the late 12th century, surrounded by several increasingly powerful Christian states. The Orthodox Slavic principalities to the East, and the Catholic Kingdom of Poland and the HRE to the West. During a period of over 150 years leading up to the arrival of German crusaders in the region, Estonia was attacked multiple times by the Slavic states, as well as Denmark and Sweden. This makes it seem that invasions of these lands were inevitable to continue even without the call for a crusade by the Pope and being led by Bishops and holy orders. Suggestions have been made that it is the perspective of the chronicler Henry of Livonia, who wrote the main source for much of these events, that all the military action in the area was due to the crusade, when that isn’t necessarily the case and much of it may have used the Papal decree of crusade as an excuse for expansion.
Christianity had already come to these areas before the crusades through the settlement of some Swedes and Danes in Latvia in the 11th century. Later there were German traders in the area who were now using the old Viking trade routes to Byzantium. Saint Meinhard of Segeberg then arrived in 1184 with the mission of converting the pagan Livonians. Although Meinhard became bishop in part of Livonia in 1186, Pope Celestine III proclaimed a crusade against the Baltic pagans in 1195.Shortly after this Meinhard died after attempting to forcibly convert local Livonians, and eventually an official crusading expedition was led by Meinhard’s successor; Bishop Berthold of Hanover, which arrived in Livonia in 1198. Shortly after arriving however, Berthold and his forces were killed by Livonians in battle. Pope Innocent III then reiterated Pope Celestine III’s call for a crusade in response in order to avenge this defeat. This time a larger force was assembled and, led by Bishop Albrecht von Buxthoeven in 1200, arrived in Livonia and set up the Bishopric of Riga in 1201, which is now the modern capital of Latvia. From here Albrecht set up the knightly order of ‘The Livonian Brothers of the Sword’ in order to aid in conversion, but perhaps more importantly to protect German trade in the area and secure German control. By 1206 the Livonian chief, who had already been baptized in 1189, was finally defeated in a decisive battle, and the Livonians were declared to be converted. The Livonian chief, Caupo, was to become an ally of the crusaders until his death in battle in 1217.
After the successful conversion of the Livonians their land was essentially taken over by the crusaders and the Bishopric of Riga. Several lucrative trading posts were taken over, and construction began of some important castles in the area; Koknese Castle and Cēsis Castle. Military alliances were also made with some nearby Latgalian principalities. The remaining Latgalians were apparently easily subdued and absorbed into the Bishopric of Riga, one of which was attacked despite already being Orthodox, the excuse being that they were in alliance with Lithuanian pagans.
In 1208 the crusaders deemed themselves ready to venture North and begin campaigns against the Estonians. Estonia at the time was comprised of serveral counties that were led by elders that loosely cooperated with each other. The crusaders began sending raids into Southern Estonian counties with the help of newly converted Livonian and Latgalian allies. The Estonian tribes however appeared to put up a fierce resistance and occasionally were found to have struck back with counterattacks at crusader held areas in Livonia. This part of the crusade was to prove more difficult than those before, and would take much longer. At various points between 1208 and 1227 armies of different sides would wreak havoc across Livonia, Latgalia and Estonia. The Livonians and Latgalians would be on the side of the crusaders or Estonians at various points, as well as the Russians of the Republic of Novgorod getting involved with either side at times. The Estonians used hill forts effectively to defend and serve as centers of each county, and these were to be besieged, captured, and re-captured multiple times.
After some time of war, both the Estonians and crusaders were becoming war weary, and so a three year truce was established from 1213 to 1215. This proved to be more advantageous to the crusaders however, as they were able to consolidate their political position effectively, whereas the Estonians were unable to bring their system of loose alliances into a centralised state. In 1217 there was finally a decisive battle and a turning point in the campaign against the Estonians. Although the Livonian leader, Caupo, died at this battle, Estonian leader and central figure of resistance, Lembitu, was also killed. Although later in 1223 there was an Estonian uprising against Christian held strongholds throughout Estonia, in some places with the help of Russian mercenaries, these places were retaken by the German crusaders in 1224. Later that year the Livonian Brothers of the Sword established their new headquarters at Viljandi in Southern Estonia.
Before the Estonian uprising, the North of Estonia was under attack from the Kingdoms of Denmark and Sweden while the South was being taken by the German crusaders. The Swedes made one failed attempt in 1220, but the Danish fleet under King Valdemar II landed in the present day capital of Tallinn and from there subjugated the whole North of Estonia. The Danes would also attempt invasions on the Estonian island of Saaremaa to the West of the mainland. Saaremaa would see off King Valdemar in 1206 and 1222 despite him attempting to establish and hold fortifications upon arrival. The Livonian Brothers of the Sword would also attack the islanders in 1216 by invading over the frozen sea, but were unsuccessful and provoked counterattacks from them. The islanders of Saaremaa would also prevent the Swedes in 1220 from keeping hold of territory in Western mainland Estonia When Swedish strongholds were completely wiped out. Eventually in the winter of 1227 the frozen sea was crossed again by crusaders, this time a 20,000 strong army which forced the surrender of multiple strongholds until the islanders of Saaremaa finally accepted Christianity. The inhabitants of Saaremaa would thrice fight back again, once in 1236, and again in 1261 when they once more renounced Christianity and killed all Germans on the Island. They were defeated once more by a joint force of the Livonian Order, forces of the Bishopric of Ösel-Wiek, and Danish Estonia. The Livonian Order then esablished a castle on the Island. The Island proved to continue to be a problem however until 1343 when the islanders arose for the last time, again killing all Germans and destroying the castle. This was recovered for the last time and remained under the Livonian Order until 1559.
As a whole the crusades, even in the general Livonian area did not end until 1290. The Curonian and Semigallian people from the Western side of the Gulf of Riga started to cause trouble, and in 1236 the Livonian Brothers of the Sword suffered a great defeat to the Semigallians. This defeat was so bad that their remnants reorganised themselves under the Teutonic Order and therefore became known as the Livonian Order. In 1242 the Livonian Order would start to conquer the Curonians but would take a long time to fully defeat them, and were even facing defeat in 1260, but they gradually subjugated them in 1267. Crusaders from Riga started the conquest of Semigallia as early as 1219, but after several unsuccessful campaigns the conquest was almost given up on in 1251. Through to the 1270s the crusaders continued to be at odds with Semigallia, and the Semigallians attacked Riga directly multiple times such as in 1280 and 1287. The last campaigns against the Semigallians took place in 1289 and 1290 when their last territories were finally taken and up to 100,000 of them migrated to Lithuania in order to continue the fight against the Germans.
The Christianization of the Eastern Baltic coasts was finally mostly complete by this time at the end of the 13th century, but it would be well into the latter part of the 14th century before the true last Pagans of Europe of Lithuania would be converted. This would prove to be one of the most complicated and lengthiest processes of Christianization in European history.