Timeline: Iran

559 BC 559 - 332BC The Achaemenian Dynasty & the Great Persian Empire which was the dominant world power for over two centuries   550BC Cyrus the Great established the First World Empire 525BC Persia conquers Egypt 332 BC Alexander the Great conquers Egypt and Persia 323 BC 323-141 BC - The Seleucid Dynasty was established by one of generals of Alexander the Great 247 BC 247 BC-224 AD The Parthians conquered the Seleucids   224 AD 224 - 642 The Sasanian Dynasty 570 The Prophet Mohammad was born 632 The Prophet Mohammad died and his teachings were compiled into the Koran, the name of the holy book of Islam   642 642 - 1220 The Arab Caliphate 1220 Mongol Era when Persia conquered by Gangis Khan 1271 The explorer Marco Polo journeyed through Persia en route to China 1295 Ghazan Khan becomes the first Mongol leader to convert to Islam 1501 1501-1524 - Safavid Dynasty founded by Shah Ismail I who united all of Persia under Iranian leadership   1795 Qajar Dynasty 1851 1851-1906 - The Qajars lost central Asian provinces to the Russians and were forced to give up all claims on Afghanistan to Great Britain   1925 1925-1940 - Pahlavi Dynasty 1979 The Shah was overthrown by the Islamic Revolution ending 2,500 years of monarchy 1980 July 29: The Islamic Revolution

http://www.history-timelines.org.uk/places-timelines/23-iran-history-timeline.htm

This was all I could find on Iran History Timeline....but I don't understand what caused Iran (in the book) to become the way it is.