The just war theory by the Medieval Christian philosopher Thomas Aquinas was developed further by legal scholars in the context of international law. Cardinal Cajetan, the jurist Francisco de Vitoria, the two Jesuit priests Luis de Molina and Francisco Suárez, as well as the humanist Hugo Grotius and the lawyer Luigi Taparelli were most influential in the formation of a "just war tradition". This just war tradition was well established by the 19th century and found its practical application in the Hague Peace Conferences and the founding of the League of Nations in 1920.