Which reasons did you include in your answer? Many people moved from rural areas to cities in search of jobs. Immigrants came to
the United States, and most settled in cities. Businesses located their factories and corporate headquarters in cities. Rail lines made transportation to and from cities easier.
The correct answer to this open question is the following.
The question is incomplete. Indeed, there is no reference to your previous answer. However, by reading the answers attached we can say that the topic is the Industrial Revolution in the United States. So all those answers can be valid because that is what happened at that time.
People that lived in rural American moved to larger cities such as New York or Chicago, where the big industries and factories were located. Those fabrics were offering plenty of jobs, although those were low-paid jobs. Immigrants came to the United States looking for better conditions for their families and they were hired in the factories. There was a negative side to all of this. Immigrants and poor people worked under unhealthy conditions in places with no ventilation. To make things worse, they lived in crowded spaces in poor neighborhoods, where the risk of disease spread was major.
The main reason was the South wanted to preserve slavery. The North wanted to abolish it. If you want some other reasons than slavery, let me know, and I will do my best to add more to this answer.
