Livonian Crusade in the context of Bishopric of Courland

The Northern Crusades or Baltic Crusades were military campaigns undertaken by Catholic Christian military orders and kingdoms in an effort to Christianize the pagan Baltic, Finnic, and West Slavic peoples around the southern and eastern shores of the Baltic Sea. In some cases, such as with the Wendish Crusade, the campaign was partly motivated to control the rich resources found in the lands.

The most notable of these campaigns were the Livonian and Prussian Crusades. Some of these wars were explicitly regarded, during the Middle Ages, as crusades; for example, the military venture against the Estonians—and the "other pagans in those parts"—authorized by Pope Alexander III's 1171 crusade bull, Non parum animus noster. However, others—such as the (possibly mythical) 12th-century First Swedish Crusade and several subsequent incursions, undertaken by Scandinavian Christians against the then-pagan Finns—were dubbed "crusades" only in the 19th century, by romantic nationalist historians.

The Lithuanian Crusade was a series of campaigns by the Teutonic Order and the Livonian Order under the pretext of forcibly Christianizing the pagan Grand Duchy of Lithuania. The Livonian Order occupied Riga in 1202 and in the 1230s they settled in Chełmno Land, a fief of Poland. They first conquered other neighboring Baltic tribes— proto-Latvians (Curonians, Semigallians, Latgalians, Selonians) and Old Prussians—in the Livonian Crusade and Prussian Crusade.

The first raid against the Lithuanians and Samogitians was in 1208. From then on, the orders played a key role in Lithuanian politics, but they were not a direct threat until the 1280s. By that time, the Grand Duchy of Lithuania was already a centralized state and could mount defenses. For the next century, the order organized annual colonialist reise (raids) into Samogitian and Lithuanian lands, without great success but at immense human cost. Border regions in Samogitia and Suvalkija became sparsely inhabited wilderness due to ethnic cleansing, although the order gained very little territory. The resulting wars between the Teutonic Order and Lithuania were one of the longest conflicts in the history of Europe.

The Battle of Lyndanisse or Lindanise was fought on 15 June 1219 during the Northern Crusades, between the forces of the invading Kingdom of Denmark and the local non-Christian Estonians. The Danish victory in the battle, at the site of the later Hanseatic city of Reval (now Tallinn, Estonia) helped King Valdemar II of Denmark to subsequently claim the territory of northern Estonia as his participation in the crusade into Estonia had been undertaken in response to calls from the Pope.

The 1219 Battle of Lyndanisse is still well known to this day, especially amongst Danes and Estonians, because of a popular legend about the first ever Danish flag, the Dannebrog, which allegedly fell from the sky, as an apparently helpful divine intervention, just when the Danish Crusaders were about to lose the battle to the local pagans.

Livonia, known in earlier records as Livland, is a historical region on the eastern shores of the Baltic Sea. It is named after the Livonians, who lived on the shores of present-day Latvia.

By the end of the 13th century, the name was extended to most of present-day Estonia and Latvia, which the Livonian Brothers of the Sword had conquered during the Livonian Crusade (1193–1290). Medieval Livonia, or Terra Mariana, reached its greatest extent after the Saint George's Night Uprising (1343–1345), which forced Denmark to sell the Duchy of Estonia (northern Estonia conquered by Denmark in the 13th century) to the State of the Teutonic Order in 1346. Livonia, as understood after the retreat of Denmark in 1346, bordered on the Gulf of Finland in the north, Lake Peipus and Russia to the east, and Lithuania to the south.

The history of Latvia began around 9000 BC with the end of the last glacial period in northern Europe. Ancient Baltic peoples arrived in the area during the second millennium BC, and four distinct tribal realms in Latvia's territory were identifiable towards the end of the first millennium AD. Latvia's principal river Daugava, was at the head of an important trade route from the Baltic region through Russia into southern Europe and the Middle East that was used by the Vikings and later Nordic and German traders.

In the early medieval period, the region's peoples resisted Christianization and became subject to attack through the Livonian Crusade. Latvia's capital city Riga, founded in 1201 by Germans at the mouth of the Daugava, became a strategic base in a papally-sanctioned conquest of the area by the Livonian Brothers of the Sword. It was to be the first major city of the southern Baltic and, after 1282, a principal trading center in the Hanseatic League.

The Sword Brethren or the Order of Sword Brothers (German: Schwertbrüderorden), formally known as The Military Brothers of Christ of Livonia (Latin: Fratres militiæ Christi Livoniae) was a Catholic military order of German crusading knights established in 1202 in Livonia by Albert, the third bishop of Riga. Pope Innocent III sanctioned the establishment in 1204 for the second time.

The membership of the crusading order comprised warrior monks, mostly from northern Germany, who fought Baltic and Finnic pagans in the area of modern-day Estonia, Latvia and Lithuania.

Terra Mariana (Medieval Latin for 'Land of Mary') was the formal name for Medieval Livonia or Old Livonia. It was formed in the aftermath of the Livonian Crusade, and its territories were composed of present-day Estonia and Latvia. It was established on 2 February 1207, as a principality of the Holy Roman Empire, and lost this status in 1215 when Pope Innocent III proclaimed it as directly subject to the Holy See.

The papal legate William of Modena divided Terra Mariana into feudal principalities: the Duchy of Estonia (dominum directum to the king of Denmark); the Archbishopric of Riga; the Bishopric of Courland; the Bishopric of Dorpat; the Bishopric of Ösel–Wiek; and territories under the military administration of the Livonian Brothers of the Sword. After the 1236 Battle of Saule, the surviving members of the Brothers merged in 1237 with the Teutonic Order of Prussia and became known as the Livonian Order. In 1346 the Livonian Order bought the Duchy of Estonia from Denmark.