stylistic:tone
Wars against Saaremaa (1206–1261)

The last Estonian county to hold out against the invaders was the island county of Saaremaa (Ösel), whose war fleets had raided 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 1216 the Livonian Brothers of the Sword and the bishop Theodorich joined forces and invaded Saaremaa over the frozen sea. In return, the Oeselians raided the territories in Latvia that were under German rule the following spring. In 1220, the Swedish army led by king John I of Sweden and the bishop Karl of Linköping conquered Lihula in Rotalia in Western Estonia. Oeselians attacked the Swedish stronghold the same year, conquered it and killed the entire Swedish garrison including the Bishop of Linköping.

In 1222, the Danish king Valdemar II attempted the second conquest of Saaremaa, this time establishing a stone fortress housing a strong garrison. The Danish stronghold was besieged and surrendered within five days, the Danish garrison returned to Revel, leaving bishop Albert of Riga 's brother Theodoric, and few others, behind as hostages for peace. The castle was razed to the ground by the Oeselians.

A 20,000 strong army under Papal legate William of Modena crossed the frozen sea while the Saaremaa fleet was icebound, in January 1227. After the surrender of two major Oeselian strongholds, Muhu and Valjala, the Oeselians formally accepted Christianity.

In 1236, after the defeat of the Livonian Brothers of the Sword in the Battle of Saule, military action on Saaremaa broke out again. In 1261, warfare continued as the Oeselians had once more renounced Christianity and killed all the Germans on the island. 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 conquering their stronghold at Kaarma. Soon thereafter, the Livonian Order established a stone fort at Pöide.