Based on the passage, what was a key consequence of the shift to assembly line production in American factories?

The rapid rise of assembly line production marked a pivotal shift in American manufacturing during the late 19th century. Factories became sites of heightened efficiency, but this came at a steep human cost. Workers were often required to perform monotonous tasks under rigorous and, at times, hazardous conditions. The assembly line system was instrumental in lowering production costs while simultaneously increasing output. Its introduction fundamentally transformed labor practices and redefined the relationship between employer and employee. This period reflects both the promise and the peril inherent in the quest for industrial progress.

• Eric Foner, The Age of Industrial America, 2000