Unions have played a vital role in American history, helping to improve working conditions and create the standard 40-hour, 5-day workweek. Since the 1950s, however, when one of three American workers belonged to a union, organized labor has been declining, dropping to one of five workers in the 1980s to just one of ten today. But unions may be on the verge of a resurgence, with employees at Amazo...