Geneva: Iran's agreement with six world powers over its nuclear program comes after decades of difficult ties between Washington and Tehran. Relations have been up, but mostly down since the 1979 Islamic Revolution and subsequent hostage crisis at the U.S. Embassy in the Iranian capital.
The nuclear agreement, designed as a first step in preventing Iran from developing a nuclear weapon in exchange for the easing of some punishing economic sanctions, signals a thaw in the U.S.-Iranian relationship.
A brief history of the long-strained relations between the United States and Iran: