Northern United States

The Northern United States, commonly referred to as the American North or simply the North, can be a geographic or historical term and definition.
Geographically, the term includes the U.S. states and regions of the United States of America that are located across the northernmost part of the country. It includes, but is not limited to, states along the Canada–United States border.
Census Bureau.
The United States Census Bureau divides some of the northernmost United States into the Midwest Region and the Northeast Region. The Census Bureau also includes the northernmost states of the Northwestern United States, that are, within the West Region.
Historical term.
Before 19th century westward expansion, the "Northern United States" was considered the present day New England region. By the 1830s it corresponded to the present day Northeastern United States
American Civil War.
During the American Civil War, the Northern United States meant the ones that remained in the United States of America, called the Union states. In this context, "The North" is the Union and "The South" is the states that seceded from the U.S. to form the Confederate States of America. However, some slave-holding states that remained in the Union may be counted on either side.