How Jews Became Germans: The History of Conversion and Assimilation in Berlin by Deborah Hertz, Yale University Press.

Karl Marx, Felix Mendelssohn and Heinrich Heine, three of  the most illustrious Germans of the 19th century, apparently had little in common.

Marx, born in Trier in 1818, was a political economist and revolutionary whose radical ideas about capitalism and a classless society spawned communism.

Mendelssohn, born in Hamburg in 1809, was a conductor and pianist whose symphonies define the Romantic era in classical music.

Heine, born in Dusseldorf in 1797, was a poet whose lyric verse still resonates and moves Germans today.

While they were very different, they  shared an alienation from their Jewish roots. Mendelssohn and Heine were converts to Christianity, while Marx hailed from a family that had already converted.

Conversion was not an uncommon phenomenon in the 19th century, when German Jews, still facing a myriad of anti-Semitic myths and restrictions that played havoc with their hopes, ambitions, dreams and careers, took the easy way out and converted to Christianity.

As Heine once famously said, conversion was his “ticket of admission into European culture.”

Heine’s dictum had its effect. By the 20th century, close to one million Christians in Germany were of Jewish origin.

Shortly after that, rabid racist Adolf Hitler assumed power in January 1933, and the new Nazi government announced laws that required all citizens to document their genealogy in full.

Determined to establish a racial state in which Jews would have no place, the Nazi regime sought to identify Christians whose ancestors had been Jewish.

Enlisting the aid of the country’s churches, the race-obsessed Nazis created the Judenkartei, a repository of conversion and intermarriage records stretching back to the mid-17th century.

Deborah Hertz’s book, How Jews Became Germans: The History of Conversion and Assimilation in Berlin, burrows into that issue by probing the lives of Jews who jettisoned Judaism and opted for Christianity in their eagerness for acceptance.

Hertz, a professor of modern Jewish history at the University of California in San Diego, focuses on a gallery of Jews within the context of German society.   She does so by exploring letters, diaries and other materials.

Among her subjects, apart from Mendelssohn, Heine and Marx, are Rahel Levin Varnhagen (1771-1833), a Berliner who hosted one of the most celebrated literary salons in Europe; Friedrich Julius Stahl (1802-1861), an ecclesiastical lawyer and politician from Munich; and Karl Ludwig Borne (1786-1837), a political writer from Frankfurt am Main who was born as Loeb Baruch.

Varnhagen, whose father was a prosperous banker and jeweller, converted in 1814 prior to her marriage to a Prussian diplomat. To Varnhagen, a self-hating Jew, conversion came as a great relief.

Her friend, the Prussian nationalist Johann Fichte, was opposed to granting Jews civil rights. His mentor, the historian Friedrich Ruhs, subscribed to a wholly ethnic view of nationhood in  which even converted Jews could not aspire to be true Germans. Ruhs’ philosophy would be adopted by Hitler and company.

Stahl, whose original name was Jolson, was baptized into the Lutheran church at 19. A church activist and a professor of law, he was known for his opposition to allowing unconverted Jews to hold civil service posts.

Borne, a convert to Lutheranism who studied constitutional law and political science, left Judaism in 1818. According to Hertz, he regarded Christianity “as integral to his identification with German national culture.”

During the 17th century, the majority of converts were poor and remained impoverished. But by the middle of the 18th century, she observes, “we meet richer converts and more extended family conversions.”

Since innumerable converts were wealthy, their departure deprived Berlin’s Jewish community of part of its operating budget.

Hertz says that “a huge proportion” of converts were infants whose parents wanted to spare them “conflicts” later in life. She adds that 60 per cent of converts between 1800 and 1874 were under the age of five.

Conversion was a tempting proposition because neither wealth nor special privileges could guarantee social acceptance in Christian circles.

Yet converts who married each other proved that baptism was not always a step on the journey to real integration, she notes.

In an intriguing aside, Hertz points out that some Jewish assimilationists delayed conversion to dabble with Reform Judaism. Having concluded that it was unsuitable, they took the final plunge.

She reminds readers, lest they need such reminders, that conversion was a temptation to some because Prussia’s treatment of Jews was dismal in comparison to the status of Jews in France.

The 1791 French Revolution emancipated Jews, but emancipation did not reach Germany until its unification in 1871 after the Franco-Prussian War.

Still, even in the wake of this watershed, German Jews flirted with conversion, a topic Hertz virtually ignores.

Faced with the fact that considerable numbers of Germans were of Jewish descent, the Nazis played God, deciding who was and who was not a certified Aryan.

As Hertz writes, “Just how many Jewish ancestors made a descendant Jewish was a topic of intense debate during the Third Reich. Surprising as it might sound, in the beginning, in 1933, the definition of who was a non-Aryan was actually broader than it became in 1935. According to the first set of regulations issued in 1933, the non-Aryan category included quarter, half, three-quarter and full Jews. Later, after the Nuremberg Laws of September 1935, all of the quarter Jews and some of the half Jews were removed from the non-Aryan category and declared to be functionally Aryans.”

The Nazis, of course, made their determination on the basis of the 60-odd narrow rectangular black volumes that comprised the Judenkartei. Hertz, having examined them in voluminous detail, avoids moral judgments about the converts until the end of her interesting book.“They wanted distinguished careers, loving marriages, a bountiful social life and an inner identity as Germans,” she states. “They could not wait for history to bring them authentic emancipation.”

But having given the converts their due, she admits that she progressively lost her sympathy for them as she stumbled upon episodes of “apparent hypocrisy, self-hatred and crass self-promotion.”