He wanted to push for job opportunities and social justice, and was eager to persuade blacks to leave the segregated, Jim Crow South for Chicago. A key part of his distribution network was made up of African-American railroad porters, who were highly respected among blacks, and by 1925 they organized a union as the Brotherhood of Sleeping Car Porters. They often sold or distributed the paper on trains. "Defender" circulation reached 50,000 by 1916; 125,000 by 1918; and more than 200,000 by the early 1920s. Credited with contributing to the Great Migration of rural southern blacks to Chicago, the "Defender" became the most widely circulated black newspaper in the country. It was known as "America's Black Newspaper." Its success resulted in Abbott becoming one of the first self-made millionaires of African-American descent; his business expanded as African Americans moved to the cities and became an urbanized, northern population. From the early 20th century through 1940, 1.5 million blacks moved to major cities in the Northeast and Mid-West.