Which of the following developments transformed the lives of millions of African Americans in the period immediately prior to the First World War through the end of the Great Depression?

This landmark Supreme Court decision, issued in 1954, declared racial segregation in public schools unconstitutional. However, it occurred well after the period specified in the question, which focuses on developments from prior to the First World War through the end of the Great Depression.

The desegregation of the armed forces was implemented in 1948 by President Harry S. Truman. This significant step towards racial equality happened long after the time frame in question and did not directly impact African Americans' lives during the earlier decades mentioned.

While sharecropping and tenant farming were prevalent in the South, they often perpetuated economic hardship and limited social mobility for African Americans rather than transforming their lives positively. This system primarily kept them in a cycle of poverty and dependence.

Though the Fourteenth and Fifteenth Amendments aimed to secure rights for African Americans, their enforcement was inconsistent during the late 19th and early 20th centuries. Many African Americans continued to face systemic discrimination and disenfranchisement, limiting the amendments' transformative potential during the specified period.