Why did the Americanization movement occur in the 20th century and not the 19th century

Americanization, in the early 20th century, activities that were designed to prepare foreign-born residents of the United States for full participation in citizenship. It aimed not only at the achievement of naturalization but also at an understanding of and commitment to principles of American life and work.

Explanation:

Before the outbreak of World War I in 1914, the American public generally took it for granted that the constant flow of newcomers from abroad brought strength and prosperity to the country. The metaphor of the “melting pot” had been introduced to symbolize the mystical potency of the great democracy, whereby people from every corner of the earth were fused into a harmonious and admirable blend. After the war began, however, American reactions to European hostilities produced an intense awareness of the aliens and “foreigners” in their midst. Assimilation, it was believed, must be achieved by the deliberate, and sometimes forceful, means of earlier nativist movements.

The Americanization movement that came into being was primarily a program of education propagated through schools, businesses, voluntary associations (such as the YMCA), libraries, and citizens bureaus. The teaching of foreigners became a favourite form of patriotic service for organizations such as the Daughters of the American Revolution, particularly after the entry of the United States into the war. The movement also took hold in nascent industries that desired an immigrant workforce capable of adjusting to mass-production work standards.

they united the colonies in their fight against the british.