Within scant decades, they'd regained Persia and soon thereafter, very nearly the balance of the territories once claimed by the Sassanid. The Safavid Empire was born.
The Sassanid's treasuries, their subjects and client kingdoms, utterly exhausted by decades of war, they could not hold against Islam's fierce harbingers. In no more than the blink of history's eye, then, the titanic Persian empire was overrun.
Al-Ghazali was a Persian theologian, philosopher, jurist and mystic, acclaimed as the most influential Muslim after the Prophet Muhammad. His works shaped how generations of Muslims would understand their religion.