The Union government (aka North) used taxes as a means to generate funding for the Civil War.
There were several different taxes put in place. One of them was a tariff known as the Morrill tariff. This tax on imported goods brought more money into the federal government. Along with this, the Union government also increased income taxes and put a higher tax on everyday items such as legal documents and alcohol. These taxes helped to pay for nearly 1/4 of the costs of the Civil War.
