The Catholic Church launched the Northern Crusades from the year of 1147,forcing the Slavs,Livonians,Estonians,Prussians,and other pagan peoples in the east of the Elbe and the eastern shores of the Baltic Sea to be integrated into the Latin Christendom.Unlike those northeastern European peoples,the Lithuanians played a long-term game with the Eastern and Western churches over the issue of religious conversion.Eventually,they accepted Catholicism through the alliance with Poland on their own initiative,rather than through passive submission after the Crusades.The Catholicisation of Lithuania has exerted a profound impact on the political landscape of Eastern Europe,not only weakening the ideological and theoretical foundations of the Northern Crusades and accelerating their end,but also changing the structure of religious power in Europe and deepening the conflicts between the Eastern and Western religions.It also constructed a mutual religious and cultural identity between Lithuania and Poland,which triggered the reorganisation of the political landscape of Eastern Europe in the 14 th-17th centuries and the formation of a new hegemony in Northeastern Europe.More than seven centuries have passed since the conversion of Lithuania to Catholicism,but its influence has not dissipated.Many of major events in modern Eastern Europe can find their origins from that historical transition.