In 1146, King Conrad III granted estates in Grindelwald to Interlaken Monastery. In the late 12th century, the barons of the alpine valleys in what became the Berner Oberland went to war against the expansionist Duke Berthold V of Zähringen. The Duke defeated a coalition of nobles in the Grindlewald valley in 1191. His victory allowed him to expand Zähringen power into the Oberland, to expand the city of Thun and found the city of Bern. Beginning in the 13th century, Interlaken Monastery began to purchase rights and land in Grindelwald and eventually forced the local nobles out of the valley. The Monastery continued to exert influence in the village and in 1315 and again in 1332 ordered the villagers to raid Unterwalden to further the political ambitions of the Abbot's patrons. In response to the raids, in 1342, Unterwalden attacked Grindelwald. A few years later, in 1348–49, the villagers joined in an unsuccessful rebellion against ecclesiastical power. In 1528, the city of Bern adopted the Protestant Reformation and proceeded to spread the new faith in Grindelwald against the populations' wishes. Berne was able to impose its will, converted the village and secularized Interlaken Abbey and the Abbey's lands. Grindelwald became part of the bailiwick of Interlaken, under a Bernese bailiff.