In order to understand Iran's desire to conquer the world, for Islam, you have to understand their view of their religion's end times. They believe, out of Iran will come thin Mahdi or Messiah who will overcome the entire world, every Government and world leader and convert ALL to Islam and rule the world from Jerusalem.
As for conversion of the world and its inhabitants to Islam it is a convert or die process led by the Mahdi and assisted by Muslim Jesus who will return to facilitate conversion of the Christians. Most current Islamic clerics believe if they can bring about world War, with the west, by the destruction of Israel, they can, and will, bring on the coming of the Mahdi even if by Nuclear means.