Why did the northern farmers favor protective tariffs

To reduce competition from foreign grain producers.

Explanation:

Protectionism is a doctrine, a theory that preaches a set of measures to be taken in favor of domestic economic activities, reducing and hindering as much as possible the import of products and foreign competition. Such a theory is used by virtually every country, to a greater or lesser extent. Based on this, northern farmers favored protectionist tariffs to reduce competition from foreign grain producers.

if you're talking about (ww2) they went bankrupt and their currency was worth nothing

explanation: