In 1239, the Barons' Crusade arrived in Palestine to help the Kingdom of Jerusalem. But it achieved little and, in 1244, Jerusalem was captured and sacked by a group of Turkish nomads. It would be nearly 700 years before a Christian army regained the city. 

Please take a look at my website nickholmesauthor.com where you can download a free copy of The Byzantine World War, my book that describes the origins of the First Crusade.