The full extent of this controversy, which has been only touched upon in previous books (including a biography I wrote in 2007), is revealed in a volume of Einstein’s correspondence and papers for 1921 that was recently published by the Princeton University Press. None of the letters is newly discovered (all are available in public archives), but most have not been published before. The 600-page volume, the 12th compiled so far by the editors of the Einstein Papers Project, pulls all of the letters and related documents together in a way that allows us now to see, even more clearly than Einstein did at the time, the political and emotional struggle he stumbled into.

Einstein was raised in a secular German Jewish household, and (except for a brief fling with religious fervor as a child) he disdained religious faith and rituals. He did, however, proudly consider himself Jewish by heritage, and he felt a strong kinship with what he called his fellow tribesmen or clansmen. His outlook in 1921 can be seen in the brusque answer he sent early that year to the rabbis of Berlin, who had urged him to become a dues-paying member of the Jewish religious community there. “In your letter,” he responded, “I notice that the word Jew is ambiguous in that it refers (1) to nationality and origin, (2) to the faith. I am a Jew in the first sense, not in the second.”

German anti-Semitism was then on the rise. Many German Jews did everything they could, including converting to Christianity, in order to assimilate, and they urged Einstein to do the same. But Einstein took the opposite approach. He began to identify even more strongly with his Jewish heritage, and he embraced the Zionist goal of promoting a Jewish homeland in Palestine.

He had been recruited by the pioneering Zionist leader Kurt Blumenfeld, who paid a call on Einstein in Berlin in early 1919. “With extreme naïveté he asked questions,” Blumenfeld recalled. Among Einstein’s queries: With their intellectual gifts, why should Jews create a homeland that was primarily agricultural? Why did it have to be its own nation-state? Wasn’t nationalism the problem rather than the solution? Eventually, Einstein came around. “I am, as a human being, an opponent of nationalism,” he told Blumenfeld. “But as a Jew, I am from today a supporter of the Zionist effort.” He also became, more specifically, an advocate for the creation of a Jewish university in Jerusalem, which became Hebrew University.

Einstein had initially thought that his first visit to the United States, which he jokingly called “Dollaria,” might be a way to make some money in a stable currency. He and his first wife had gone through a bitter divorce, and they were still fighting over finances. Hamburg banker Max Warburg and his New York–based brother Paul tried to help Einstein line up lucrative lectures. They asked both Princeton and the University of Wisconsin for a fee of $15,000. In February of 1921, Max Warburg informed him, “The amount you wish is not possible.” Einstein was not terribly upset. “They found my demands too high,” he told his friend and fellow physicist Paul Ehrenfest. “I am glad not to have to go there; it really isn’t a pretty way to make money.” Instead, he made other plans: he would go to Brussels to present a paper at the Solvay Conference, the preeminent European gathering of physicists.