Final answer:
Unions have been most successful in organizing within the manufacturing and government sectors, with significant representation by several major unions among government employees. The service sector has seen relatively less union success.
Step-by-step explanation:
Historically, unions have had the most success in organizing within the manufacturing and government sectors. In the manufacturing industry, unions have traditionally been strong, peaking in job numbers in the late 1970s before experiencing a decline. On the other hand, the government sector has seen several of the biggest unions form, including the American Federation of State, County and Municipal Employees (AFSCME), the Service Employees International Union (SEIU), and the National Education Association (NEA). These organizations demonstrate the significant union presence among government employees. Conversely, in the service sector, unions have not achieved the same level of organization and influence compared to the manufacturing and government arenas.