Explanation: Poland was long-Catholic, but Lithuania was one of the last pagan holdouts in Europe. For this reason, a crusade was undertaken by the Teutonic Knights (of horned helmets fame) to convert Lithuania... BY THE SWORD!
Poland, however, managed to convince Lithuania to convert mostly-peaceably instead, and formed the Polish-Lithuanian Commonwealth. This did not stop the Teutonic Order's wars which involved mass plundering and total conquest of the Baltic. Curious! Wars, naturally, ensued with the Commonwealth, which the Teutonic Order eventually lost.