It was part of the wave of pogroms that swept across the Russian Empire after tsar's October Manifesto in the wake of the abortive Revolution of 1905.
[1][2] The pogrom started as a right-wing demonstration against tsar's Manifesto, which turned into an attack on the Jewish quarter.
[3] The pogrom was resisted by Jewish self-defense groups, with partial success.
Instrumental in organizing the self-defense was the Kishinev branch of Tze'irei Zion, who issued a circular calling Jewish youth to organize the resistance to violence.
[4] Between 1902 and 1905 the number of Jews in Kishinev decreased from about 60,000 to 53,000 due to emigration.