Protective tariffs are as much applications of force as are blockading squadrons, and their object is the same—to prevent trade. The difference between the two is that blockading squadrons are a means whereby nations seek to prevent their enemies from trading; protective tariffs are a means whereby nations attempt to prevent their own people from trading. What protection teaches us, is to do to ourselves in time of peace what enemies seek to do to us in time of war.

Ch. 6. - Protection or Free Trade? (1886)