In the late eighteenth and early nineteenth centuries, Jews throughout Europe lobbied their respective governments for emancipation. Having for centuries been regarded as non-citizens without any rights, the Jews, influenced by the Haskalah's emphasis on equality and integration, began to demand from their rulers citizenship and treatment equal to that of non-Jewish residents. The cause of emancipation, which began to be implemented on a permanent basis in the mid- and late-nineteenth century, was greatly hurt in 1819 by a series of anti-Jewish disturbances known as the "Hep Hep riots."
For some time, sporadic anti-Jewish violence had been accompanied by the rallying call "Hep! Hep!" The origins of this phrase are unclear – while some hold that the cry was an acronym for "Hierosolyma est perdita," a Crusader chant meaning "Jerusalem is lost," others believe that it was simply as an exhortatory cry for sheep-herders that was borrowed by Jew-baiters. In either case, the slogan became a widespread one in 1819 when German Jews were the targets of widespread rioting.
The immediate cause of these riots probably lay in the Jewish demands for civil rights. The Jewish representatives who attended the 1815 Congress of Vienna formally demanded emancipation, and German academics and politicians alike responded with vicious opposition. The Jews were portrayed to the public as "upstarts" who were attempting to take control of Europe, particularly of its financial sector. This widespread lie, combined with the fact that many Europeans, reeling from the famine of 1816, were heavily indebted to Jewish bankers and moneylenders, sparked violence beginning in Wuerzburg in August of 1819. The attacks on Jews and Jewish property spread from there to the whole of Germany, with particularly vicious conflict occurring in Frankfurt, Leipzig, Dresden, and Darmstadt. Eventually, the rioting reached as far as Denmark and Poland.
The local German authorities invariably responded to the disturbances by protecting the Jews; in several cases, they even called in the military to hold back rioters. However, the government's reaction was not entirely favorable to the Jews. While they protected them physically, many rulers used the attacks as pretexts not to grant equal rights to Jews, explaining that if even the suggestion of such a move was provoking popular unrest, the actual granting of such rights would lead to catastrophe.
The riots had two simultaneous effects on the German Jews. In many cases, the violence sped the Jews' attempts at assimilation and integration into secular society. Proponents of emancipation refused to be dissuaded, and believed that only if Jews became fully "German" would they be treated as such. The riots also led some Jews to form even more tightly knit groups in response to the animosity from without; the Verein fuer Kultur und Wissenschaft der Juden (Association for Culture and Science of the Jews) was one such group.
Eventually, emancipation was achieved despite the popular unrest; nonetheless, the granting of equal rights probably took longer than necessary because of the rioting. By the mid-1800s, the Hep! Hep! cry had lost its popularity, as even more virulent expressions of anti-Semitism became prevalent.
"Hep Hep." Encyclopedia Judaica
Mendes-Flohr, Paul, and Judah Reinharz, The Jew in the Modern World: A Documentary History. Oxford University Press. New York, 1995.