Julius Martov was a Menshevik rather than a Bolshevik. The major
difference between the two factions was that Martov believed the
revolution should happen according to classic Marxian line, i.e.,
by the workers as a large group. Lenin felt that the revolution
should be by a small group of professional revolutionaries with a
large group of followers.
Martov recognized that the October Revolution was not a true
Marxian Revolution but more of a plain military coup by Lenin and
the Bolsheviks. Martov wanted a revolution by the workers not a
revolution by a small political party.
He also feared that once the Bolsheviks got into full power,
they would keep all governmental power for themselves and exclude
all other political parties and opinions, which is just what they
did.