The key moments in the long history of U.S.-Iran tensions

Officials from Britain, Russia, China, France, Germany, the European Union, the United States and Iran wait for the start of a meeting on Iran's nuclear program in Lausanne, Switzerland, on March 30, 2015. (Brendan Smialowski/Pool via AP)

In Lausanne, Switzerland, top-level negotiators from Iran and a number of world powers are still wrangling over the outline of a deal that they hope will ease tensions surrounding Tehran's controversial nuclear program. Such a deal also could be a prelude to a historic diplomatic rapprochement between the United States and Iran, two countries that share a long, turbulent history of friendship, antagonism and strife.