Answer :
Although there were many factors, the greatest was "an increase in the number of factories and jobs". Industrialization had begun in the United States, opening up many more factory positions.
The correct answer is an increase in the number of factories and jobs.
The North's population growth before the Civil War can be contributed to industrialization. At this time, businesses were beging to use technology and machines that resulted in a high demand for unskilled workers. These workers needed to merely be able to repeat small tasks on a consistent basis. This is why a large amount of people moved to the North, as these jobs provided stability.