The fourth Crusade started in 1202 and lasted two years, approximately 8 years after the third Crusade had ended.
The Third crusade had been a complete disaster and the fourth Crusade began with renewed determination.
The mission of the fourth Crusade was to recapture Jerusalem from the Muslim Egyptians who now controlled the important Holy city.
Once again it was the Pope who demanded the holy city of Jerusalem to be recaptured, the newly elected Pope Innocent III was determined to reclaim the holy city of Jerusalem by force, as this was the only option left to the crusaders of the west.
The disastrous third Crusade had destroyed any trust between the religions and there was no chance of any negotiation.
In 1203 the Crusader armies of the fourth Crusade forgot their initial mission pledges of recapturing the Holy lands from the Egyptian Muslims after their leaders struck a deal with the Byzantine Prince Alexios Angelos.
The Prince asked the Crusaders of the fourth Crusade to make his father the Emperor of Constantinople once again, once in power his father would give the Crusaders military and financial assistance to complete their fourth Crusade’s mission.
The Crusaders agreed to this, thinking that the additional help they received would guarantee their success in capturing the Holy lands.
However the offer of support for the Crusaders that had been promised was short lived as there was a uprising in Constantinople and Alexios Angelos was quickly forced from power and was eventually murdered.
The Crusaders of the fourth Crusade did not receive any more payments for the services that they had provided.
After the murder of Alexios Angelos the goal of the fourth Crusade completely changed and instead of recapturing Jerusalem the Crusaders had a change of heart and decided upon conquering and taking for themselves Constantinople along with help from the Venetians crusaders.
Although the Crusaders of the fourth Crusade with help from the Venetians had captured large parts of the Byzantine Empire there were still many areas that they had not been conquered such as Nicaea, Trebizond etc.
This is where the resistance built up that eventually overcame and drove the conquering armies of the fourth Crusade and the Venetians out of Constantinople.
The third Crusade had been a disaster and there were great hopes for the fourth Crusade, however yet again things had not gone to plan and indiscipline and greed was seen to have destroyed the best laid plans of the Crusaders.
Not only that but the Crusader armies had made a terrible mistake in attacking and looting one of the greatest metropolis that survived in the Christian world.
The mainly Christian Venetian soldiers and sailors who attacked Constantinople had overcome its mighty walls of the city that was known as the Queen of cities and was very important to the Eastern Orthodox Church.
The attack on Constantinople by the fourth Crusade armies was the start of the decline of the Byzantine Empire as it divided the Eastern Orthodox church and the Western Roman Catholic Church, the fourth crusade attack strained this relationship and there was little trust between both sides after this event.
The fourth Crusade started off with what was considered to be a noble cause of the Church to reclaim the holy lands of the city of Jerusalem from the Muslim Egyptian occupiers.
The third Crusades ended badly and the betrayal and capture of the previously supportive city of Constantinople led to the beginning of the end for any future Crusades to recapture the holy lands from the Muslim occupiers.
The relationship between the Eastern Orthodox Church and the Roman Catholic Church was damaged beyond repair.