That the talks are even happening represents a historic moment, given the decades of enmity between the two countries since the 1979 Islamic Revolution and the U.S. Embassy hostage crisis.

At risk is a possible American or Israeli military strike on Iran’s nuclear sites, or the Iranians following through on their threats to pursue an atomic weapon.

A second round of negotiations between Iran and the United States over Tehran’s rapidly advancing nuclear program ended Saturday after several hours of talks, Iranian and American officials said.