The Northern Crusades or Baltic Crusades were crusades undertaken by the Catholic kings of Denmark and Sweden, the German Livonian and Teutonic military orders, and their allies against the pagan peoples of Northern Europe around the southern and eastern shores of the Baltic Sea. Swedish and German campaigns against Russian Eastern Orthodox Christians are also sometimes considered part of the Northern Crusades.  Some of these wars were called crusades during the Middle Ages, but others, including most of the Swedish ones, were first dubbed crusades by 19th century romantic nationalist historians. The east Baltic world was transformed by military conquest: first the Livs, Letts and Estonians, then the Prussians and the Finns underwent defeat, baptism, military occupation and sometimes extermination by groups of Germans, Danes and Swedes.
The official starting point for the Northern Crusades was Pope Celestine III's call in 1193; but the already Christian kingdoms of Scandinavia and the Holy Roman Empire had started to move to subjugate their pagan neighbors even earlier. The non-Christian peoples who were objects of the campaigns at various dates included:
- the Polabian Slavs and Sorbs (by the Saxons, Danes, and Poles, beginning with the Wendish Crusade)
- the peoples of (present-day) Finland in 1154 (Finland Proper; disputed), 1249? (Tavastia) and 1293 (Karelia) (Swedish Crusades, although Christianization had started earlier),
- Estonians, Latgalians, and Livonians (by the Germans and Danes, 1193–1227),
- Lithuanians (by the Germans, unsuccessfully, early 14th century-1316),
- Curonians and Semigallians,
- Old Prussians,
- Polabian Wends and Abotrites (between the Elbe and Oder rivers).
Armed conflict between the Balts and Slavs who dwelt by the Baltic shores and their Saxon and Danish neighbors to the North and south had been common for several centuries prior to the crusade. The previous battles had largely been caused by attempts to destroy castles and sea trade routes and gain economic advantage in the region, and the crusade basically continued this pattern of conflict, albeit now inspired and prescribed by the Pope and undertaken by Papal knights and armed monks.
The campaigns started with the 1147 Wendish Crusade against the Polabian Slavs (or "Wends") of what is now northern and eastern Germany. The crusade occurred parallel to the Second Crusade to the Holy Land, and continued irregularly until the 16th century.
Subjugation of Livonians, Latgalians, and Estonians
By the 12th century, the peoples inhabiting the lands now known as Estonia, Latvia and Lithuania formed a pagan wedge between increasingly powerful Christian states – Orthodox to their east and Roman Catholic to their west. The difference in creeds was a reason they had not yet been effectively converted.Template:Fact During a period of more than 150 years leading up to the arrival of German crusaders in the region, Estonia was attacked 13 times by Russian principalities, and by Denmark and Sweden as well. Estonians for their part made raids upon Denmark and Sweden. There were peaceful attempts by the western Christians to convert the Estonians, starting with missions dispatched by Adalbert, Archbishop of Bremen in 1045-1072. However, these peaceful efforts seem to have had very limited success.
Moving in the wake of German merchants who were now following the old trading routes of the Vikings, a monk named Meinhard landed at the mouth of the Daugava river in present-day Latvia in 1180 and was made bishop in 1186. The Pope proclaimed a crusade against the Baltic heathens in 1193 and a crusading expedition led by Meinhard's successor, Bishop Berthold, landed in Livonia (part of present-day Latvia, surrounding the Gulf of Riga) in 1198. Although the crusaders won their first battle, Bishop Berthold was mortally wounded and the crusaders were repulsed.
In 1199, Albert of Buxhoeveden was appointed by the Archbishop of Bremen to Christianise the Baltic countries. By the time Albert died 30 years later, the conquest and formal Christianisation of present-day Estonia and northern Latvia was complete. Albert began his task by touring the Empire, preaching a Crusade against the Baltic countries, and was assisted in this by a Papal Bull, which declared that fighting against the Baltic heathens was of the same rank as participating in a crusade to the Holy Land. Though he landed in the mouth of the Daugava in 1200 with only 23 ships and 500 soldiers, the bishop's efforts ensured that a constant flow of recruits followed. The first crusaders usually arrived to fight during the spring and returned to their homes in the autumn. To ensure a permanent military presence, the Livonian Brothers of the Sword were founded in 1202. The founding by Bishop Albert of the market at Riga in 1201 attracted citizens from the Empire and economic prosperity ensued. At Albert's request, Pope Innocent III dedicated the Baltic countries to the Virgin Mary to popularise recruitment to his army and the name "Mary's Land" has survived up to modern times.
The Livonians, who had been paying tribute to the East Slavic Principality of Polotsk, at first considered the Germans as useful allies. The first prominent Livonian to be christened was their leader Caupo of Turaida. As the German grip tightened, the Livonians rebelled against the crusaders and the christened chief but the uprising was put down. Caupo of Turaida remained ally of the crusaders until his death in the Battle of St. Matthew's Day in 1217. 
The Germans turned their attention to the Latvian tribes to the east in Latgalia. By 1208, the Germans were strong enough to begin operations against the Estonians, who were at that time divided into eight major and several smaller counties led by elders with limited co-operation between counties. In 1208-27, war parties of the different sides rampaged through Livonia, Latgalia and different Estonian counties, with Livonians and Latgalians normally as allies of the Crusaders and East Slavic Principalities appearing as allies of different sides at different times. Hill forts, which were the key centres of Estonian counties, were besieged and captured a number of times. A truce between the war-weary sides was established for three years (1213-1215) and it proved generally more favourable to the Germans, who consolidated their political position, while the Estonians were unable to develop their system of loose alliances into a centralised state. The Livonian leader Kaupo was killed in battle near Viljandi (Fellin) on 21 September 1217, but the battle was a crushing defeat for the Estonians, whose leader Lembitu was also killed. Since 1211, his name had come to the attention of the German chroniclers as a notable Estonian elder and he became the central figure of the Estonian resistance.
The Christian kingdoms of Denmark and Sweden were also greedy for conquests on the Eastern shores of the Baltic. While the Swedes made only one failed foray into western Estonia in 1220, The Danish Fleet headed by King Valdemar II of Denmark had landed at an Estonian town of Lindanisse  (present-day Tallinn) in 1219. After Battle of Lyndanisse the Danes established a fortress, which was besieged by Estonians in 1220 and 1223, but held out. Eventually, the whole of northern Estonia was in Danish hands.
The last Estonian county to hold out against the invaders was the island county of Saaremaa, whose war fleets had raided Denmark and Sweden during the years of fighting against the German crusaders. A 20,000 strong army under Papal legate William of Modena crossed the frozen sea while the Saaremaa fleet was icebound, in January 1227. Following the defeat of the Estonians, the crusade moved against the Curonians and the Semigallians, Baltic tribes living to the south and west of the river Daugava.
Prussia and Lithuania
Campaigns of Konrad of Masovia
Konrad I, the Polish Duke of Masovia, unsuccessfully attempted to conquer pagan Prussia in crusades in 1219 and 1222. Taking the advice of the first Bishop of Prussia, Christian of Oliva, Konrad founded the crusading Order of Dobrzyń (or Dobrin) in 1220. However, this order was largely ineffective, and Konrad's campaigns against the Old Prussians were answered by incursions into his territory of Culmerland (Chełmno Land). Subjected to constant Prussian counter-raids, Konrad wanted to stabilize the north of the Duchy of Masovia in this fight over border area of Chełmno Land. Masovia had only been conquered in the 10th century and native Prussians, Yotvingians, and Lithuanians were still living in the territory, where no settled borders existed. His military weakness led Konrad to invite the Teutonic Knights to Prussia.
The Northern Crusades provided a rationale for the growth and expansion of the Teutonic Order of German crusading knights which had been founded in Palestine at the end of the 12th century. Due to Muslim successes in the Holy Land, the Order sought new missions in Europe. Duke Konrad I of Masovia in west-central Poland appealed to the Knights to defend his borders and subdue the pagan Baltic Prussians in 1226. After the subjugation of the Prussians, the Teutonic Knights fought against Poland and the Grand Duchy of Lithuania.
When the Livonian knights were crushed by Lithuanians in the Battle of the Sun in 1236, coinciding with a series of revolts in Estonia, the Livonian Order was inherited by the Teutonic Order, allowing the Teutonic Knights to exercise political control over large territories in the Baltic region. The Teutonic Knights failed to subdue pagan Lithuania, which officially converted to (Catholic) Christianity in 1386 on the marriage of Grand Duke Jogaila to the 11-year-old Queen Jadwiga of Poland. Polish-Lithuanian forces defeated the Teutonic Knights thoroughly at the Battle of Grunwald in 1410.
The Teutonic Order's attempts to conquer Orthodox Russia (particularly the Republics of Pskov and Novgorod), an enterprise endorsed by Pope Gregory IX, can also be considered as a part of the Northern Crusades. One of the major blows for the idea of the conquest of Russia was the Battle of the Ice in 1242. With or without the Pope's blessing, Sweden also undertook several crusades against Orthodox Novgorod.
Notes and references
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- An Historical Overview of the Crusade to Livonia by William Urban
- The Northern Crusades: Second Edition by Eric Christiansen; p.93; ISBN 0140266534
- TheChronicle of Henry of Livonia ISBN 0231128894
- Template:Dk icon SALMONSENS KONVERSATIONS LEKSIKON
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