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.
History of Western civilization
In 1095, Pope Urban II called for a Crusade to re-conquer the Holy Land from Muslim rule, when the Seljuk Turks prevented Christians from visiting the holy sites there. For centuries prior to the emergence of Islam, Asia Minor and much of the Mid East had been a part of the Roman and later Byzantine Empires. The Crusades were originally launched in response to a call from the Byzantine Emperor for help to fight the expansion of the Turks into Anatolia. The First Crusade succeeded in its task, but at a serious cost on the home front, and the crusaders established rule over the Holy Land. However, Muslim forces reconquered the land by the 13th century, and subsequent crusades were not very successful. The specific crusades to restore Christian control of the Holy Land were fought over a period of nearly 200 years, between 1095 and 1291. Other campaigns in Spain and Portugal (the Reconquista), and Northern Crusades continued into the 15th century. The Crusades had major far-reaching political, economic, and social impacts on Europe. They further served to alienate Eastern and Western Christendom from each other and ultimately failed to prevent the march of the Turks into Europe through the Balkans and the Caucasus.