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 up to the Smoot–Hawley Tariff Act of 1930, were set by Congress after many months of testimony and negotiations. In 1934, the U.S. Congress, in a rare delegation of authority, passed the Reciprocal Tariff Act of 1934, which authorized the executive branch to negotiate bilateral tariff reduction agreements with other countries. The prevailing view then was that trade liberalization may help stimulate economic growth. However, no one country was willing to liberalize unilaterally. Between 1934 and 1945, the executive branch negotiated over 32 bilateral trade liberalization agreements with other countries. The belief that low tariffs led to a more prosperous country are now the predominant belief with some exceptions. Multilateralism is embodied in the seven tariff reduction rounds that occurred between 1948 and 1994. In each of these "rounds", all General Agreement on Tariffs and Trade (GATT) members came together to negotiate mutually agreeable trade liberalization packages and reciprocal tariff rates. In the Uruguay round in 1994, the World Trade Organization (WTO) was established to help establish uniform tariff rates.