The original Nuclear Arms Deal ended many or Iran's nuclear activities up to 2026 and then terminated in 2031. In the meantime, as this article explains, they busied themselves with developing a ballistic missile program which one would have to presume was for the day when they started back developing nuclear weapons. The original agreement was only a delay in the development of nuclear weapons. Iran wanted desperately to remove the international sanctions and assumed once they were off that they would never be reimposed. One of many reasons for remaining engaged in the Middle East.