 Complete the following phrase:  In 1199, Pope Innocent III declared a crusade to defend the Christians of Livonia. Fighting reached Estonia in 1206, when Danish king Valdemar II unsuccessfully invaded Saaremaa. The German Livonian Brothers of the Sword, who had previously subjugated Livonians, Latgalians, and Selonians, started campaigning against the Estonians in 1208, and over next few years both sides made numerous raids and counter-raids. A major leader of the Estonian resistance was Lembitu, an elder of Sakala County, but in 1217 the Estonians suffered a significant defeat in the Battle of St. Matthews Day, where Lembitu was killed. In 1219, Valdemar II landed at Lindanise, defeated the Estonians in the 