"A customs duty is a tax on commodities crossing a political boundary. A tariff, technically, is a schedule of such taxes, but the terms are often used interchangeably. In American politics, the "tariff question" was a major, often passionate, political issue from the dawn of the Republic until modern times.

A tariff can serve several purposes: like all taxes, it can raise money to pay the costs of government; it can protect domestic goods from foreign competition; and it can seek to force a foreign country to change a policy....

[In 1897], the tariff was raised to an average of 57 percent on the value of imported goods in the Dingley Tariff of 1897, the highest in the nation's history. But high tariffs at home tended to generate high retaliatory tariffs abroad, crimping American exports. As American industry matured, it did not need to fear foreign competition as much, and tariffs were moderated beginning in 1909, when the Payne-Aldrich Tariff lowered rates to an average of 38 percent...."

(Source: The Reader's Companion to American History, edited by E. Foner and J.A. Garraty. Published in Boston by Houghton Mifflin. ©1991.)