Name a major labor organization formed in the 1950s that sought to unite different unions.

The American Federation of Labor and Congress of Industrial Organizations (AFL-CIO) is the correct answer because it was established in 1955 through the consolidation of two major labor organizations: the American Federation of Labor (AFL) and the Congress of Industrial Organizations (CIO). This merging aimed to create a more unified front for the labor movement in the United States, allowing for greater strength and coordination among different unions. The AFL-CIO sought to represent a wide array of workers across various industries and sectors, advocating for workers' rights, better wages, and improved working conditions.

This unification was significant at a time when the labor movement was facing various challenges, both politically and socially, and helped establish the AFL-CIO as a dominant force representing the interests of millions of American workers. This contrasts with the other organizations mentioned, such as the National Labor Union, which was formed in the 19th century and did not unify unions in the 1950s; the Industrial Workers of the World, which focused on a different approach to labor organization, emphasizing direct action and worker control; and the Teamsters Union, which is a specific union for truck drivers and logistics workers and did not serve the broader goal of uniting multiple unions under one umbrella