The Arab conquest of Persia, led to the end of the Sassanid Empire in 644, the fall of the Sassanid dynasty in 651 and the eventual decline of the Zoroastrian religion in Iran. Arabs first attacked the Sassanid territory in 633, when general Khalid ibn Walid invaded Mesopotamia, which was the political and economic center of the Sassanid state. Following the transfer of Khalid to the Roman front in the Levant, the Muslims eventually lost their holdings to Iranian counterattacks. The second invasion began in 636 under Saad ibn Abi Waqqas, when a key victory at the Battle of Qadisiyyah led to the permanent end of Sassanid control west of Iran. The Zagros mountains then became a natural barrier and border between the Rashidun Caliphate and the Sassanid Empire. Owing to continuous raids by Persians into the area, Caliph Umar ordered a full invasion of the Sassanid Iranian empire in 642, which was completed with the complete conquest of the Sassanids by mid 644. The quick conquest of Iran in a series of well coordinated multi-pronged attacks, directed by Caliph Umar from Medina several thousand miles from the battlefields in Iran, became his greatest triumph, contributing to his reputation as a great military and political strategist. Wikipedia [ - ]

The Arab conquest of Persia, led to the end of the Sassanid Empire in 644, the fall of the... [ + ]