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150 A HISTORY OF THE CRUSADES II 
 It needed only Venetian ambition to give direction to the hostile forces
waiting to take advantage of Byzantine difficulties. The dismemberment of
the empire would ensure the maritime supremacy of Venice, which in the course
of the twelfth century had from time to time been threatened by Byzantine
imperial policy and by the antagonism of the Greek people. The Fourth Crusade
could have presented no surprise in western diplomatic circles. In fact,
the internal condition of the empire did in several respects favor such an
attack. In the past scholars have stressed the weakness of the dynasty of
the Angeli and the hostility and greed of Byzantium's Latin enemies. But
in reality a prime cause in determining the course of events was the fundamental
change in the character of the empire from the eleventh century onwards.
This was largely due to separatist and centrifugal forces, which were continually
undermining the central authority; such forces were enormously accelerated
by the method of land holding based on grants in pronoia which bore a marked
similarity to the western feudal system. 
 Thus weakened, the empire was no match for its western enemies. When Alexius
III considered the strength of the crusading host, actually bent on restoring
his imprisoned and blinded brother to his throne, he fled with what portable
funds he could lay hands on. Nicetas Choniates, who disliked him, said that
he was too cowardly to attempt any defense of the city as his son-in-law
Theodore Lascaris wished. <36> And so Isaac II was again placed on
the throne with his son Alexius IV as co-emperor. But it was an impossible
position for the unfortunate Angeli: the hovering Latins continually pressed
them for funds, which they could not easily raise, while the populace resented
and feared the influence of the westerners. Both Greek and Latin sources
tell of continual tension and of constant clashes and skirmishes which came
to a climax on January 1, 1204, with the Greek attempt to send fire-ships
against the Venetian fleet. "This, then, was the way in which Alexius
repaid us for all that we had done for him," wrote Villehardouin. <37>
The Greeks, for their part, reproached Alexius IV for his failure to control
the crusaders; terrified of his own people, the young emperor even thought
of admitting the French and Italians into the palace of the Blachernae for
his own defense. At this, Alexius Ducas "Mourt zouphlus", another
son-in-law of Alexius III, promptly seized the throne in late January 1204.
He had Isaac and Alexius IV im- 
 36 Nicetas Choniates, Historia (CSHB), p. 720. 
 37 Geoffrey of Villehardouin, La Conqu8te de Constantinople, chap. 220.