In 1096, four armies from various European regions started making their way eastward to help the Byzantine Empire. While the armies were amassing, a smaller, less organized group of commoners and knights decided to mount a “People’s Crusade” and, against the Emperor’s advice, made their way into Muslim territory. This was officially the first attack of the Crusades. As you can imagine, it went poorly. The Turkish armies demolished the unprepared crusaders.
When the main armies were ready, they mounted their own assault on the Turks. The strength of the allies was overwhelming and led to the capture of Syrian Antioch in 1098 and eventually Jerusalem in 1099.
While the first official, armed Crusade was a success, it created a massive divide between the religious groups in the area. Many of the Crusaders took the war as a Christian push for supremacy. The mentality was, “If they’re not Christians, they’re enemies.” Many innocent people, including Jews who had nothing to do with the Crusades, were massacred in the name of progress. And, of course, the Islamic Empire was not pleased to lose so much territory.