Final answer:
Union membership in the United States declined due to less friendly laws for union formation, the passage of laws protecting workers' rights, and cultural differences.
Step-by-step explanation:
Union membership in the United States declined for several reasons. One important factor was the passage of laws that made it less friendly for workers to form unions. In the 1930s, the National Labor-Management Relations Act was passed, which gave workers the right to organize unions.
However, after World War II, the Taft-Hartley Act allowed workers to opt out of union membership, making it harder for unions to form.
Another reason for the decline of union membership is the passage of laws aimed at protecting workers' rights. These laws reduced the need for unions as they provided workers with better work conditions, overtime regulations, parental leave, and pension regulations.
Lastly, there are cultural differences between countries that affect union membership. The United States has lower union membership compared to other developed economies partly due to different attitudes towards unions in the workplace.