Six of the world's major powers (the so-called P5 plus one) reached a historic phased agreement with Iran to limit its nuclear development to peaceful uses. It's difficult to overstate this accomplishment, which bridges 33 years of broken diplomatic relations between the U.S. and Iran. The change has come as the result of an intense, unrelenting campaign of tough sanctions, military warnings and secret negotiations by President Obama and U.S. allies.It is equal in importance to President Ronald Reagan's historic breakthrough with the Soviet Union on nuclear weapons.