Immigration and high infant survival rates which in turn cause increase in population are the two main factors that led to the increase in size of the workforce.
Step-by-step explanation:
Immigration is the major factor for increase in the work force. During industrialization, people in the country side started to immigrate to the cities in search of greener pasture which would increase the standard of living and hence urbanization took place.
People were much interested in settling near the industries. Due to automation, there was increase in standard of living which paved way for the decreased level of mortality rate in infants. This caused an increase in population which led to the larger size of the workforce.