Final answer:
When the U.S. refuses to sell goods to Iran over concerns about terrorism, it is engaging in sanctions, specifically an economic boycott or embargo. This is a strategic move meant to influence Iran's policies, arising from historical tensions and ideological differences between the two countries.
Step-by-step explanation:
When the United States refuses to sell goods to Iran because of the perception that the country harbors radicals and terrorists, the refusal is most accurately referred to as a sanction. These sanctions serve as a form of punishment and are used to influence a country's policies or actions. For instance, the United States has imposed an economic boycott and nearly a total trade embargo on Iran in response to various concerns, including its nuclear program and support for groups considered as terrorists by the U.S. government.
An instance of alleviating such measures was the Iran nuclear deal, which aimed to curb Iran's nuclear activities in exchange for the lifting of economic sanctions, thus allowing trade to resume. However, historical tensions, such as the 1979 revolution and the ensuing hostage crisis, have contributed to the strained U.S.-Iran relations and the establishment of an embargo. Further complicating the relationship are geopolitical concerns and ideological differences, as well as Iran's internal policies that conflict with Western notions of democracy and human rights.