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.
History of taxation in the United States
Tariffs have played different roles in trade policy and the economic history of the United States. Tariffs were the largest source of federal revenue from the 1790s to the eve of World War I, until it was surpassed by income taxes. Since the revenue from the tariff was considered essential and easy to collect at the major ports, it was agreed the nation should have a tariff for revenue purposes.