The journey taken to the Holy land to take land back from the Muslims was the Crusade. When the Turks took control they started to stop letting Christian pilgrims in.
Pope Urban's speech was made here, urging rescue of the holy land. This was the Council of Clermont. This was the beginning of the first crusade and the speech was held in 1095.
The Seljuk Turks were the group that stopped Christians from visiting the Holy Land in 1071. They prosecuted many Christians, mostly in Syria and Palestine.
The Third Crusade was led by 3 kings. This was till 1189-1192. This did not learn to Richard the Lionheart getting Jerusalem, but the pilgrims could now visit the Holy Land.
The First Crusade was led by unskilled peasants and knights in 1096-1099. This was the Crusade that was the most successful and got the Turks out of Jerusalem.
The Fourth Crusade was led by French knights and went against the Pope. This took place during 1202-1204 and the Crusaders actually ended up taking Constantinople instead of the Holy Land.
