Even though it was a period with a very large immigrant population, the United States in the 1920s was undergoing a period dominated by nativist attitudes. World War I triggered many xenophobic anxieties in the country. Many Americans wondered how patriotic the overall population could really be with so many immigrants among them. In many ways, the fate of Nicola Sacco and Bartolomeo Vanzetti can be viewed as a microcosm of this.
These two men were both Italian immigrants and anarchists. In the eyes of many native-born white Americans, these were two strikes against them. In the post-WWI isolationist years, many Italians and other recent immigrants fell victim to the xenophobia in the country. Italians in particular were looked upon with suspicion; for being Catholics, they were particularly hated by such groups as the Ku Klux Klan. The 1920s was a time of revival for this nativist hate group. They began to focus their attention and ire on the immigrant communities of the North.
It did not help the defendants that they were known members of anarchist organizations. Many of these groups had significant Italian numbers, and therefore many Americans linked Italians and anarchists closely in their minds. Witnesses to the murders often could not agree on many details. However, many reported that the criminals were Italian. What made them think this is unclear. At any rate, that was enough circumstantial evidence for many to link Sacco and Vanzetti to the crime.
The early 1920s was also the time of the Red Scare. While they were not Communists, Sacco and Vanzetti were caught up in the same overall hysteria. The Bolshevik Revolution in Russia caused many Americans to suspect immigrants, particularly those from eastern and southern Europe, of harboring seditious motives. At the same time, increasing numbers of labor strikes and social protests, often with a large immigrant component, had many afraid that there were those ready to start a revolution in America. As anarchists and Italians, Sacco and Vanzetti fit right into the popular imagination of murderous foreigners.
We may never know for sure if these two men were actually guilty. However, it is clear that the prejudices of the day meant that these two men were robbed of a fair trial. The police, prosecution, judge, and jury were influenced by strong nativist and anti-Italian attitudes that were prevalent at the time.