Military history of the Crusader states
The Seljuk–Crusader War began when the First Crusade wrested territory from the Seljuk Turks during the Siege of Nicaea in 1097 and lasted until 1128 when Zengi became atabeg of Aleppo. At the latter date, the chief threat to the Crusaders from the east and north became the Zengids. The conflict was generally fought between European Crusaders and the Seljuk Turks and their vassals. The Muslim Syrian emirates occasionally allied themselves with the Christians against rival states.
Religious war
During the time of the Crusades, some of those who fought in the name of God were recognized as the "Milites Christi", soldiers or knights of Christ.
The Crusades were a series of military campaigns that took place during the 11th through 13th centuries against the Muslim Conquests. Originally, the goal was to recapture Jerusalem and the Holy Land from the Muslims, and support the besieged Christian Byzantine Empire against the Muslim Seljuq expansion into Asia Minor and Europe proper. Later, Crusades were launched against other targets, either for religious reasons, such as the Albigensian Crusade, the Northern Crusades, or because of political conflict, such as the Aragonese Crusade. In 1095, at the Council of Clermont, Pope Urban II raised the level of war from "bellum iustum" ("just war"), to "bellum sacrum" ("holy war"). In 16th-century France there was a succession of wars between Roman Catholics and Protestants (Hugenots primarily), known as the French Wars of Religion. In the first half of the 17th century, the German states, Scandinavia (Sweden, primarily) and Poland were beset by religious warfare in the Thirty Years War. Roman Catholicism and Protestantism figured in the opposing sides of this conflict, though Catholic France did take the side of the Protestants but purely for political reasons.