US Industries that required large labor forces are on the decline, and therefore unions are on the decline as well. Manufacturing, Steel working, Mining, etc are gone by the wayside for the most part. We as a nation arent constructing new bridges, tunnels, interstate systems, railways, that require the manpower of the 1940s. And if we do need to build something we import the materials so machines can assemble it. Advances in technology mean that building a bridge in the year 2012 requires a fraction of the people that it required in the 1940s.