The main story of unions during the past half-century in the United States is the sharp decline in union membership to only 7% of private sector workers, and the equally sharp growth of union membership to 36% of all government employees. Nor are these trends unique to America; for example, union members declined to about 15% of all British private sector workers, and unions are much more important among public-sector workers.
Unions declined over time in the private sector in most developed countries partly because of the shift from manufacturing with large plants, where unions have been strong, to the service sector with small establishments, where unions have been weak. Other factors reducing unionization include the growth of competition from imports, and the sharp expansion over time of the welfare state. The latter has meant that governments are providing medical benefits and other services that had been provided by unions. As Posner indicates, an important reason for the growth of unions among government employees has been the expansion of government. This expansion increased the number of government employees, and gave them a more powerful voice as voters, and as contributors to political campaigns.
(photo credit: Bernard Pollack)