 Between 1881 and the outbreak of the First World War, an estimated 2.5 million Jews left Russia - one of the largest group migrations in recorded history.After the Pesach pogrom of 1903, pogroms became the official policy of the Russian Empire, and the anti-Semitic terror reached its peak in October 1905.Jan Gotlib Bloch (1836-1901) a wealthy railroad magnate and researcher on warfare and society converted to Calvinism, the religion of a small minority in the Russian Empire.