Crusades
The term "crusade" used in modern historiography at first referred to the wars in the Holy Land beginning in 1095, but the range of events to which the term has been applied has been greatly extended, so that its use can create a misleading impression of coherence, particularly regarding the early Crusades. The term used for the campaign of the First Crusade was "iter" "journey" or "peregrinatio" "pilgrimage". The terminology of crusading remained largely indistinguishable from that of pilgrimage during the 12th century, reflecting the reality of the first century of crusading where not all armed pilgrims fought, and not all who fought had taken the cross. It was not until the late 12th to early 13th centuries that a more specific "language of crusading" emerged. Pope Innocent III used the term "negotium crucis" "affair of the cross" for the Eastern Mediterranean crusade, but was reluctant to apply crusading terminology to the Albigensian crusade. The "Song of the Albigensian Crusade" from about 1213 contains the first recorded vernacular use of the Occitan "crozada". This term was later adopted into French as "croisade" and in English as "crusade". The modern spelling "crusade" dates to c. 1760. Sinibaldo Fieschi (the future pope Innocent IV) used the terms "crux transmarina" for crusades in Outremer against Muslims and "crux cismarina" for crusades in Europe against other enemies of the church. Medieval Armenian term for Crusades — xacˇ‘e˘nkalk‘.
List of sources for the Crusades
Greek Orthodox historians:
Michael Psellos, Anna Komnene, John Kinnamos, Niketas Choniates, Nicephorus Gregoras, George Acropolites.
The Eastern Orthodox view of the Crusades is dominated by the sack of Constantinople and the establishment of the Frankokratia in the Fourth Crusade in 1204. While the First Crusade was declared upon the request of the Byzantine Emperor, and concluded in triumphal success, the Crusades as a whole 
resulted in the terminal decline of the Byzantine Empire. Although the Byzantine Emperors were restored in 1260,
the empire could never fully recover until eventually, weakened by civil wars, it fell to the Ottomans in 1453.