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
Tariffs have historically served a key role in the nation's foreign trade policy and as a source of federal income. Tariffs were the greatest (approaching 95% at times) source of federal revenue until the Federal income tax began after 1913. For well over a century the federal government was largely financed by tariffs averaging about 20% on foreign imports.