Prior to the civil war more people living in the cities of what region than any other region

Northwest, JK its Northeast

Prior to the civil war more people living in the cities of what region than any other region was the North East Region of the United States.

Explanation:

For much of the United States history up till the civil war, the country's political and economic power remained in the North East.

This mostly included the 13 original colonies, which were densely populated, industrialized and rich.

However, after the Civil War ended, places such as Florida, California, etc began to prosper and a whole mid-west region (centered around Chicago) and a West coast region (centered around San Francisco) gradually began to have economic importance.