<human>:  Why did the Greek Revolution of 1821 fail?
<bot>: The revolution failed because the Greeks were unable to unite behind a single leader. The revolution was started by the Filiki Eteria, a secret society of Greek intellectuals. The Filiki Eteria was formed in 1814, but the revolution did not begin until 1821. The Filiki Eteria had a number of different goals, including the liberation of Greece from Ottoman rule and the establishment of a constitutional monarchy.