In 1195 Alexius III Angelus, Isaac II's brother, usurped the throne. Isaac was blinded and thrown into a dungeon in Constantinople. Though his government was no improvement. Anarchy prevailed at Constantinople as well as elsewhere in its few dominions.
But now the Fourth Crusade began, proving perhaps one of the greatest farces in the history of mankind.
The bad blood Isaac had created with the west during the Third Crusade now was to come and haunt Constantinople.
Having gathered in Venice the great army became heavily indebted to the Venetians. Was the original idea of the crusaders an attack on Egypt, the Venetians, who were to provide the transport for the crusaders, very much to their own profit, suggested an attractive change of programme. A business proposition by which the Venetian fleet and the crusading lords were to share in the profits.
The totally destabilized Constantinople offered an easy prey.
And so the Fourth Crusade, composed to fight the 'infidels of the east' resulted in the attack upon the most populous Christian city on the face of the earth.
Isaac II Angelus, restored(reign 1203-1204) &
Alexius IV Angelus (reign 1203-1204) With the Crusaders still outside the city, Alexius III losthis nerve and fled. This left the people of Constantinople to free his blinded brother and restore him the throne.
Under the pressure from the crusaders Isaac's son Alexius IV, who was the pretender the crusaders had wished to see on the throne, was crowned co-emperor.
Though soon after hostilities should resume between the two sides.
Alexius V Ducas (reign 1204) The troubles, fires and riots which ensued under the joint rule of the enfeebled Issac II and the western 'puppet emperor' Alexius IV, with the crusaders at the gates, led eventually to their overthrow. Alexius Ducas, son of the previous emperor Alexius III Ducas, seized the throne for himself.
Alexius IV was strangled and Isaac II is said to have died of grief at the news of the murder of his son.
No sooner was Alexius V in command he began to energetically lead the city in its defence against the crusaders. Had he been in charge at the time of the arrival of the Crusade, the invaders would most likely have been repulsed. But now it was too late. Despite the valiant efforts of Alexius V the city fell on 12/13 April 1204.