Iran
The centuries-long geopolitical and ideological rivalry between Safavid Iran and the neighboring Ottoman Empire, led to numerous Ottoman–Persian Wars. The Safavid Era peaked in the reign of Abbas the Great, 1587–1629, surpassing their Ottoman arch rivals in strength, and making the empire a leading hub in Western Eurasia for the sciences and arts. The Safavid Era saw the start of mass integration from Caucasian populations into new layers of the society of Iran, as well as mass resettlement of them within the heartlands of Iran, playing a pivotal role in the history of Iran for centuries onwards. Following a gradual decline in the late 1600s and early 1700s, which was caused by the internal conflicts, the continuous wars with the Ottomans, and the foreign interference (most notably the Russian interference), the Safavid rule was ended by the Pashtun rebels who besieged Isfahan and defeated Soltan Hosein in 1722.

Q: Safavid Iran peaked during whose reign?
Abbas the Great