Final answer:
The 100 percent Americanism doctrine was primarily supported by nativist and white supremacist groups, as they rallied behind a homogeneous and exclusionary vision of America predominantly shaped by White Anglo-Saxon Protestant values.
Step-by-step explanation:
The term "100 percent Americanism" references a movement that emphasized a vision of the United States as a homogeneous nation, typically defined by White Anglo-Saxon Protestant (WASP) values. This ideal was often exclusionary, aiming to preserve a certain image of America against the perceived threat posed by immigrants and various ethnic, religious, or racial groups. The groups that were most associated with supporting the 100 percent Americanism doctrine were nativist and white supremacist groups, as they sought to protect their vision of what being an American meant, often at the expense of immigrants and non-White populations. Such groups included the revived Ku Klux Klan of the 1920s, which pushed for rigid immigration restrictions and promoted a nativist ideology that largely consisted of anti-immigrant, anti-Catholic, and anti-Semitic sentiments. Their ideology aligned with the broader nativist movement, which contributed to policies favoring northern European immigrants over those from other regions.
Labor unions and farmers' cooperatives, civil rights and women's rights organizations, and religious fundamentalists and social gospel societies typically had their own separate aims and did not principally rally behind the 100 percent Americanism doctrine. In summary, it is the nativist and white supremacist groups that are most connected to the support of the 100 percent Americanism doctrine.