In 1230, following the Golden Bull of Rimini, Grand Master Hermann von Salza and Duke Konrad I of Masovia launched the Prussian Crusade, a joint invasion of Prussia intended to Christianise the Baltic Old Prussians. The Order then created the independent Monastic State in the conquered territory, and subsequently conquered Livonia. The Kings of Poland accused the Order of holding lands rightfully theirs.
The Order lost its main purpose in Europe with the Christianisation of Lithuania. The Order became involved in campaigns against its Christian neighbours, the Kingdom of Poland, the Grand Duchy of Lithuania, and the Novgorod Republic (after assimilating the Livonian Order). The Order had a strong economic base, hired mercenaries from throughout Europe to augment their feudal levies, and became a naval power in the Baltic Sea. In 1410, a Polish-Lithuanian army decisively defeated the Order and broke its military power at the Battle of Grunwald (Tannenberg). The Crusade by this Order, once completed, would control all of the Baltic, including what would become the very powerful state of Prussia