In 1391, the escalating persecution suffered by Iberian Jewry led to mass conversions, which continued as the Jews’ situation worsened. The presence of large populations of former Jews, and the return of some of their descendants to Judaism in subsequent generations, challenged the way both Jews and Gentiles understood Jewish identity. David Graizbord explains how:

By . . . 1415, some half to two-thirds of Castilian and Aragonese Jews had become titular Christians. Irrespective of the sincerity [of their conversions], or lack thereof, in many if not most cases the converts and their immediate, baptized descendants still lived among, or relatively close to, Jews and had extensive social, economic, and familial relations with them. This meant that for the first time, the religion and the ethnicity of tens of thousands of people once known and still widely regarded as “Jews” were at odds: these “New Christians” were “Jewish” as concerned their social and economic relations, their ethnic culture, and their social reputation, yet their religious identity was at least theoretically identical to that of the majority population.

Of particular interest in this connection is the promulgation as early as 1436 of private and municipal statutes of “Purity of Blood.” This concept formally recast and stigmatized Jewishness as a matter of descent rather than of official religious status, much less of demonstrable belief and behavior. Equipped with this new notion of purity, “Old Christians” began to treat questions of morality and religious fealty as matters of familial heredity.

For their part, Jews acquired a correspondingly acute consciousness of their genealogy. . . . Jewish letters of introduction from the late 1300s and early 1400s, [i.e. from when mass conversion began], differ from older ones in explicitly distinguishing between “good” Jewish families—that is to say, families whose members had not converted—and families sullied by Christianization. A fateful message of the letters was that while Iberian Jews may share ethnicity, their differing fealty to God rendered them essentially separate. What now mattered for purposes of determining a Jew’s character as a Jew, was not only the quality of his or her behavior as an observer of mitzvot, but the caliber of his or her yiḥus [lineage].

In its dedication to bringing totalitarianism into the 21st century, the Chinese Communist party has developed high-tech forms of surveillance using facial-recognition software, a vast system of “social credit,” and careful control over its subjects’ cellular phones. Even stricter and more invasive measures are applied to the Uyghurs of the northwestern part of the country. Beijing is also happy to export its innovations in tyranny to allies like Iran and Russia. Playing a key role in these advances is a nominally private company called Tiandy Technologies. Craig Singleton describes its activities:

Both Tiandy testimonials and Chinese-government press releases advertise the use of the company’s products by Chinese officials to track and interrogate Uyghur Muslims and other ethnic minorities in China’s Xinjiang province. According to human-rights groups, Chinese authorities also employ Tiandy products, such as “tiger chairs,” to torture Uyghurs and other minorities.

Iran has long relied on China to augment its digital surveillance capabilities, and Tehran was an early adopter of Beijing’s “social-credit” system, which it wields to assess citizens’ behavior and trustworthiness. . . . Iranian government representatives have publicized plans to leverage smart technologies, including AI-powered face recognition, to maintain regime stability and neutralize dissent. Enhanced cooperation with China is central to those efforts.

At present, Tiandy is not subject to U.S. sanctions or export controls. In light of Tiandy’s operations in both Xinjiang and Iran, policymakers should consider removing the company, its owner, and stakeholders from the international financial system and global supply chains.