Great depression, and 2/3rds drop in global trade resulted.

I present also 1828 dementia https://en.wikipedia.org/wiki/Tariff_of_Abominations which started southern secessionist movements.

Unjustifiable trade attacks like all wars are bad for unity. If California or Texas has to pay $10k more per car so metal and auto workers elsewhere get high pay, national unity fractures. Everything being super expensive with no jobs because of global trade retaliations, means that Mexicans stop being a unifying problem, and those white Michigan and Pennsylvania blue collar workers cheering for Trump are the problem. Better cars elsewhere in the world become a bigger national unity factor the more protection $ is spent on inferior cars.