[6] Henry wrote that the papacy's use of the crusade as a foreign policy was extended to include military expeditions against the Livonians for the first time by papal proclamation in c. 1195, and then renewed in 1197 or 1198.

[7] There are no independent sources to confirm this; the earliest surviving papal letter on the Livonian crusade dates from 5 October 1199, issued by Pope Innocent III.

[7] Most surviving documents relating to William of Modena's mission as legate deal with problems caused by rivalries and internal tensions within the Catholic Church in Livonia and neighbouring areas.

The indigenous Livonians (Līvi), who had been paying tribute to the East Slavic Principality of Polotsk,[20] and were often under attack by their southern neighbours the Semigallians, at first considered the Low Germans (Saxons) to be useful allies.

When peaceful means of conversion failed to produce results, the impatient Meinhard plotted to convert Livonians forcibly but was thwarted.

By 1208 the important Daugava trading posts of Salaspils (Holme), Koknese (Kokenhusen) and Sēlpils Castle (Selburg) had been taken over as a result of Albert's energetic campaigning.

In 1209 Albert, leading the forces of the Order, captured the capital of the Latgalian Principality of Jersika, and took the wife of the ruler Visvaldis captive.

By 1208 the Crusaders were strong enough to begin operations against the Estonians, who were at that time divided into eight major and seven smaller Counties, led by elders, with limited co-operation between them.

With the help of the newly converted local tribes of Livs and Latgalians, the crusaders initiated raids into Sakala and Ugaunia in Southern Estonia.

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.

King John I of Sweden tried to establish a Swedish presence in the province of Wiek, but his troops were defeated by the Oeselians in the Battle of Lihula in 1220.

At the end of the year Pope Honorius III announced the appointment of Bishop William of Modena as papal legate for Livonia, Prussia, and other countries.

The last Estonian county to hold out against the invaders was the island country of Saaremaa (Ösel), whose war fleets had continued to raid Denmark and Sweden during the years of fighting against the German crusaders.

In 1206, a Danish army led by the king Valdemar II and Andreas, the Bishop of Lund, landed on Saaremaa and attempted to establish a stronghold, without success.

In 1220, a Swedish army led by the king John I of Sweden and the bishop Karl of Linköping captured Lihula in Rotalia in Western Estonia.

In 1222, the Danish king Valdemar II attempted the second conquest of Saaremaa, this time establishing a stone fortress housing a strong garrison.

The stronghold was besieged and surrendered within five days, the Danish garrison returning to Revel while leaving Bishop Albert of Riga's brother Theodoric and others behind as hostages for peace.

In 1241 the Oeselians once again accepted Christianity by signing treaties with the Livonian Order's Master Andreas de Velven and the Bishopric of Ösel-Wiek.

This was followed by a treaty signed in 1255 by the Master of the Order, Anno Sangerhausenn, and, on behalf of the Oeselians, elders whose names were phonetically transcribed by Latin scribes as Ylle, Culle, Enu, Muntelene, Tappete, Yalde, Melete, and Cake.

A peace treaty was signed after the united forces of the Livonian Order, the Bishopric of Ösel-Wiek, and Danish Estonia, including mainland Estonians and Latvians, defeated the Oeselians by capturing their stronghold at Kaarma.

On 24 July 1343 the Oeselians arose yet again, killing all the Germans on the island, drowning all the clerics, and besieging the Livonian Order's castle at Pöide.

Following the defeat of the Estonians, the crusade moved against Curonians and Semigallians, Baltic tribes living to the south and west of the Daugava river and closely allied with Samogitians.

After the defeat of Estonians and Osilians in 1227, the Curonians were confronted by Lithuanian enemies in the east and south, and harassed by the Livonian Brothers of the Sword from the north; in the west, on the sea-shore, their arch-enemies, the Danes and Swedes, were lurking, waiting for an opportunity.

In this hopeless situation, further aggravated by famine, the Curonians preferred to try to make peace with the Christian conquerors, inviting the monks into their country thereby escaping attacks by the Scandinavian nations.

In 1207, the Semigallian duke Viestards (Latin: dux Semigallorum) helped the christened Livonian chief Caupo conquer back his Turaida Castle from pagan rebels.

During the Battle of Karuse on the frozen Gulf of Riga, the Livonian Order was defeated, and its master Otto von Lutterberg was killed.

More than 40 knights were killed, including the master of the Livonian Order Willekin von Endorp, and an unknown number of crusader allies.

On 7 June 1238, by the Treaty of Stensby, the Teutonic knights returned the Duchy of Estonia to Valdemar II, until in 1346, after St. George's Night Uprising, the lands were sold back to the order and became part of the Ordensstaat.