The Civil War was about protectionism, not slavery. Slavery was a throw in, a bargaining chip.
The protectionists won the Civil War.
Um...yeah... and John Brown broke into the arsenal at Harper's Ferry to fight Walmart. Uh huh, yeah that's it.
But yes, the industrial and manufacturing North generally supported free trade. In fact even earlier than the Civil War, many New Englander's contemplated secession (see the Hartford Convention) because they hated Thomas Jefferson's anti-foreign trade policies, particularly the Embargo Act of 1807 and James Madison's Non-Intercourse Act of 1809.