[Luis Gonzalez]

The biggest reason for the "loss" of manufacturing jobs is increased productivity as a result of advancements in technology.

Less people can make more things than ever before.

[EQAndyBuzz]

It is safe to add that to the equation. An example:

The company I worked for had a cafeteria with 19 employees. All Union. The company asked for a reduction of 1 or 2 employees to be removed to cut costs. Not to fire them, just to move them. The union refused and chose to fight after the company made a compelling argument that the positions somewhere else would serve the company better.

A couple of days later, vending machines showed up in the cafeteria. All 19 employees were fired.

Technology :)