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.
Rhineland massacres
Previous to the Crusades, the Jews were divided among three major areas which were largely independent of one another. These were the Jews living in Islamic nations (still the majority), those in the Byzantine Empire and those in the Roman Catholic West. With the persecutions that began around 1096, a new awareness of the entire people took hold across all of these groups, reuniting the three separate strands.