United States national emergency with respect to Iran was first declared on 14 November 1979. At least 11 executive orders were based on this emergency state. The emergency which was renewed in 2016 for the 36th year, is the "oldest existing state of emergency." The renewal of the emergency state with respect to Iran was equal to continuation of non-nuclear US sanctions against Iran.
By 2014, this state of emergency was among 30 others which US was dealing with. According to Gregory Korte of USA Today, this state of emergency gives "extra ordinary powers" to the president to "seize property, call up the National Guard and hire and fire military officers at will," since it's declared by executive order. The language of such declarations are "nearly apocalyptic," according to the USA today. Although bound by law to review the emergence declarations, congress provides little "oversight" on them, said Korte.
2016 renewal
According to the White House, some of those "executive orders that were issued pursuant to this national emergency" were terminated by the time JCPOA was implemented. However, the situation was extended by Obama for an additional year, as he believed that US relations with Iran had not yet returned to normal, and the process of implementing the agreements with Iran, dated Jan. 19, 1981, Algiers Accords, had not been fully implanted. "Despite the historic deal to ensure the exclusively peaceful nature of Iran's nuclear program, certain actions and policies of the Government of Iran continue to pose an unusual and extraordinary threat to the national security, foreign policy, and economy of the United States," wrote Obama in his letter to the Congress.
Most of the U.S. sanctions against Iran are legally originated from this state of emergency. This renewal meant that "non-nuclear US sanctions against Iran will remain in effect for at least another year."