Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
Tariff in United States history
The tariff history of the United States spans from 1789 to present. The first tariff law passed by the U.S. Congress, acting under the then-recently ratified Constitution, was the Tariff of 1789. Its purpose was to generate revenue for the federal government (to run the government and to pay the interest on its debt), and also to act as a protective barrier around newly starting domestic industries. An Import tax set by tariff rates was collected by treasury agents before goods could be unloaded at U.S. ports.