During the Civil War Era (between the 1800s- 1860s) the blue states (the North) were

During the Civil War era in the 1860s, the states that comprised the Union, often referred to as the "blue states" in modern terms, were the Northern states. These Northern states were opposed to secession and were committed to preserving the Union. Some of the key Northern states included states in the Northeast (such as New York, Pennsylvania, and Massachusetts), the Midwest (such as Ohio, Illinois, and Michigan), and parts of the West.

The term "blue states" is a contemporary designation used to identify states that generally lean towards the Democratic Party in modern political contexts. However, during the Civil War era, the distinction was not based on political party affiliations but rather on the geographic alignment with the Union. The states that remained loyal to the Union during the Civil War were the Northern states, and they played a crucial role in the conflict against the seceding Southern states, known as the Confederate States.