… is from chapter 3 of William Graham Sumner’s 1885 book, Protectionism: the -ism Which Teaches that Waste Makes Wealth :
The contact of trade slowly saps old national prejudice and religious or race hatreds. The jealousies which were perpetuated by distance and ignorance can not stand before contact and knowledge. To stop trade is to arrest this beneficent work, to separate mankind into sections and factions, and to favor discord, jealousy, and war.
Not only is protectionism uncivilized because it employs threats of violence to block peaceful commerce among consenting adults, it is uncivilized also because it obstructs and distorts the expansion of civilization across political borders. Protectionism is an expression of antediluvian and uncivilized tribalism. It is a manifestation of humanity’s worst and most self-destructive instincts.