Final answer:
The NAACP, established in 1909, had grown substantially by 1920 through its advocacy for civil rights and legal challenges against segregation, though the exact membership is not specified.
Step-by-step explanation:
The National Association for the Advancement of Colored People (NAACP) was founded in 1909 and quickly emerged as a pivotal civil rights organization. By 1920, the NAACP had grown significantly in membership as it championed for the rights of African Americans nationwide. It not only provided a platform for political advocacy but also launched numerous legal challenges against segregation, seeking to enforce the rights promised in the 14th and 15th Amendments.
Although the exact number of members by 1920 is not specified in your materials or widely documented, it's clear that the NAACP had garnered a substantial following due to its active role in combating racial injustice and advocating for civil rights.