This long period of 120 years was a troubled one. Tīmūr's attack on Iran, which began in 782/1380–1 with the invasion of Khurāsān and Sīstān, terminated the pre-Timurid interregnum in a period characterised by sudden alarms. Even after the conqueror Tīmūr's death, except for the comparatively peaceful reign of Shāh Rukh (807–850/1405–1447), conditions throughout the land remained unsettled; his successors could not be at peace one with another; government was the plaything of turbulent rivals. Besides numerous princes of the Timurid dynasty, there were other leaders on the scene, such as those of two Türkmen dynasties, the Qarā Quyūnlū and Āq Quyūnlū, who had established themselves in the regions of Āzarbāījān and western Persia, with occasional inroads into the eastern regions of the country. Eventually this state of affairs was ended in the east by the Shaibanids and in the west by the Safavids.

Disturbances that can be dated back to the Mongol invasions, and which finally developed into the disruption and disorder of the period after Shāh Rukh's death, occasioned a serious decline in civilisation and deterioration in thought. At the beginning of this period a few of the scholars, poets and writers of the interval between the Mongol Īl-Khāns and the Timurids were still alive and affording contributions to science and literature. But apart from these few, and with the possible exception of those who had gathered at the court of Sultān Husain Bāīqarī at Heart and who were didactic rather than original, we hardly hear of any important or justly celebrated men of learning or science until the latter part of the 9th/15th century.