Question

why did northern industrialists favor tariffs?

Answer 1

Although it's often exaggerated, the North had a slight advantage over the South in terms of industrialization -- something which the South came to rely on with it's slightly more agrarian economy. The North, however, was yet still not readily able to compete with England, whose rapidly developing industry could comparatively produce more goods in less time for a lower cost. Many Southerners turned to the English to provide many of these industrial goods (e.g. those used in farming), which hurt business for the Northern industrialists. As a result, the North felt that tariffs would be better for solidarity by maintaining a consistent level of demand from the South, virtually free of competition from industrially superior nations -- which would enable them to mature faster and boost the over-all US national economy. This school of economic thought is known as protectionism. As you can guess, the South were not very willing to be forced to be "robbed" by the North...