"Taking of Jerusalem by the Crusaders, 15th July 1099", (oil on canvas), Signol, Emile (1804-92) / Château de Versailles, France / Giraudon / The Bridgeman Art Library
The Crusade was a Catholic military expedition called by Pope Urban II to reconquer the Holy Land invaded by Muslims between 632 and 661. It actually started as a pilgrimage and ended in a military action.
Capture of Jerusalem by Godfrey of Bouillon, First Crusade, 15 July 1099. Liebig
The Byzantine Emperor Alexius I Comnenus, based in the then Constantinople (now Istanbul) called for urgent help to Pope Urban II to send volunteers to repel the invading Seljuk Turks, from Anatolia (now Turkey) who tried to invade the Byzantine Empire, also it is known as the Eastern Roman Empire.
On June 7th, 1099, the Crusaders reached their goal, the city of Jerusalem. The city was in no position to defend itself.
More than 15 thousand soldiers between knights and peasants joined the First Crusade by land and sea to get to Constantinople and then go to Jerusalem, stormed the city and massacred equally to Muslims, Christians and Jews. After the bloody feast, the Crusaders established the Kingdom of Jerusalem, the County of Tripoli, the Principality of Antioch, and the County of Edessa. So they created what they called The Crusader States.
The military success of the First Crusade from 1095 till 1099 at the fall of Jerusalem can be considered as a major military success.
The First Crusade 1095 – 1099
Jerusalem had been outside the Christian rule for some 461 years and forcible capture, decided not to deliver the lands conquered the Byzantine emperor, reopened for international trade, which was lost with the fall of the Western Roman Empire in the 476.
There were 9 crusades in total and the proceeds lasted a little less than 200 years.