Jews played highly visible roles, over an extended period, in the leadership of leftist movements – including socialist, communist, and anarchist organizations – around the world. In the first half of the twentieth century, significant numbers of Jews were also evident in the rank and file of specific left-wing political parties. In addition to participating in general leftist movements, Jews in Eastern Europe created and fostered a number of distinctive Jewish socialist parties with tens of thousands of members. Why were so many Jews sympathetic to left-wing causes? Explanations revolving around the purported characteristics of Jews, the impact of Jewish religious ideas, and the marginality of the Jewish population have been expounded by prominent scholars. However, there is reason to question both of the first two of these explanations. At the present time, left-wing ideas no longer hold the same degree of attraction for Jews as they did one hundred years ago. The relationship of Jews to the left was historically contingent, specific to political, historic, and economic conditions that prevailed between the late-nineteenth and mid-twentieth centuries in Europe, and that impacted upon Jewish political opinion in the United States and other countries that received large numbers of Jewish immigrants from Europe.

In a book that first appeared in 1911, the German sociologist Robert Michels noted “the abundance of Jews among the leaders of the socialist and revolutionary parties” and attempted to illuminate this phenomenon by reference to “specific racial qualities” that “make the Jew a born leader of the masses, a born organizer and propagandist.” Michels asserted that among these qualities were “sectarian fanaticism which, like an infection, can be communicated to the masses with astonishing frequency; next we have an invincible self-confidence (which in Jewish racial history is most characteristically displayed in the lives of the prophets) … remarkable ambition, an irresistible need to figure in the limelight, and last but not least an almost unlimited power of adaptation.” He cites examples of “the quantitative and qualitative predominance of persons of Hebrew race” in leftist parties in Germany, Austria, the United States, Holland, Italy, Hungary, Poland, and other lands, and adds that Jewish involvement with socialist parties is also linked to the “spirit of rebellion against the wrongs from which” Jewry suffers, that is, the Jewish response to continuing antisemitism.