The 1920s witnessed a backlash against immigration in the United States as part of a general, nationwide outpouring of xenophobia. Although America had always been a land of immigrants, the vast majority of the huge influx of newcomers in the late nineteenth and early twentieth centuries were noticeably different; they simply did not talk, act, or look like traditional Americans. For one thing, they did not speak English. Another factor that aroused nativist hostility was their religion. Many of the newcomers were Jews or Roman Catholics, making them the object of fear and loathing for large numbers of American Protestants. The great wave of immigration of the late nineteenth and early twentieth centuries sparked fears that the whole complexion of American society was changing--and not for the better.
The subsequent backlash took many different forms. At the level of government policy, the Immigration Act of 1924 instituted a strict quota system that severely limited immigration from certain parts of the world, most notably Asia. On a completely different level, the exponential growth of the Ku Klux Klan, both in terms of its membership and political power, showed that increasing numbers of Americans were prepared to rally to the cause of "100% pure Americanism" even if it involved violence and murder.
The increasingly toxic political environment formed the backdrop to the notorious case of Sacco and Vanzetti. They were Italian immigrants accused of committing murder in the course of an armed robbery. They were also—crucially—political radicals, anarchists who had actively campaigned against World War One. In the popular mind, anarchism was associated with extremists who represented a danger to the very foundations of society. More to the point, anarchism was regarded as an alien ideology, a foreign import brought into the United States by the recent wave of mass immigration.
As far as the facts of the case are concerned, the evidence against Sacco and Vanzetti was flimsy to say the least. But in the prevailing atmosphere of xenophobia and hostility toward any political movement that was in the least bit progressive or radical, that was very much a minor consideration. It soon became clear that Sacco and Vanzetti were on trial not just for the crimes they were alleged to have committed, but also for their status as immigrants and political radicals. The presiding judge made no pretense of impartiality, openly showing his hostility and contempt for the defendants and their political beliefs.
When the guilty verdicts were duly delivered, there was a sense of inevitability about it despite the notable lack of hard evidence submitted by the prosecution. Sacco and Vanzetti were formally convicted—and subsequently executed—for murder. But in substance, they were condemned to die because they were thought of as not belonging in the United States: both by virtue of their status as Italian immigrants and their commitment to an "un-American" way of thinking. Sacco and Vanzetti were not the first or the last victims of the xenophobic backlash that engulfed the United States in the 1920s. But their case was by far the most famous, not least because it encapsulated all the various social, economic, and political tensions developing in America at that time.