 Complete the following phrase:  League membership gradually stabilized throughout the 1920s and 1930s as the league adopted progressively more formal organization. The first official championship game was held in 1933. The NFL stopped signing black players in 1927 but reintegrated in 1946 following World War II. Other changes followed after the war; the office of league President evolved into the more powerful Commissioner post, mirroring a similar move in Major League Baseball. Teams became more ficially viable, the last team folding in 1952 and the league absorbing teams from the briefly more successful All-America Football Conference in 1950, of which only the San Francisco 49ers and the Cleveland Browns survive to the present day. By 1958, when 