The Doctrine developed further in the 15th century after the conflict between the Teutonic Knights and Poland to control 'pagan' Lithuania. At the Council of Constance (1414), the Knights argued that their claims were "authorized by papal proclamations dating from the time of the Crusades allowed the outright confiscation of the property and sovereign rights of heathens." The council disagreed, stating that non-Christians had claims to rights of sovereignty and property under European natural law. However, the council upheld that conquests could 'legally' occur if non-Christians refused to comply with Christianization and European natural law. This effectively meant that peoples who were not considered 'civilized' by European standards or otherwise refused to assimilate under Christian authority were subject to war and forced assimilation: "Christians simply refused to recognize the right of non-Christians to remain free of Christian dominion."