After the Crusades from the West that resulted in the instability of the Islamic world during the 11th century, a new threat came from the East during the 13th century: the Mongol invasions. In 1206, Genghis Khan from Central Asia established a powerful Mongol Empire. A Mongolian ambassador to the Abbasid Leader in Baghdad is said to have been murdered, which may have been one of the reasons behind Hulagu Khan’s sack of Baghdad in 1258.
The Mongols and Turks from Central Asia conquered most of the Eurasian land mass, including both China in the east and parts of the old Islamic empire and Persian IslamicKhwarezm, as well as Russia and Eastern Europe in the west, and subsequent invasions of the Levant. Later Turkic leaders, such as Timur, though he himself became a Muslim, destroyed many cities, slaughtered thousands of people and did irreparable damage to the ancient irrigation systems of Mesopotamia. On the other hand, due to the lack of a powerful leader after the Mongolian invasion and Turkish settlement, some local Turkish kingdoms appeared in the Islamic world and they were in war and fighting against each other for centuries. The most powerful kingdoms among them were the empire of Ottoman Turks, who became Sunni Muslims and the empire of Safavi Turks, who became Shia Muslims. Eventually, they invaded very wide parts of the Islamic world and entered in a competition and a series of bloody wars until the middle of 17th century.
Traditionalist Muslims at the time, including the polymath Ibn al-Nafis, believed that the Crusades and Mongol invasions were a divine punishment from God against Muslims deviating from the Sunnah. As a result, the falsafa, some of whom held ideas incompatible with the Sunnah, became targets of criticism from many traditionalist Muslims, though other traditionalists such as Ibn al-Nafis made attempts at reconciling reason with revelation and blur the line between the two. However Saladin rejected the widespread belief of divine punishment and instead blamed Muslims for committing a series of errors in their policies (regarding social stability) and on the battlefield.
Eventually, the Mongols and Turks that settled in parts of Persia, Central Asia, Russia and Anatolia converted to Islam, and as a result, the Ilkhanate, Golden Horde and Chagatai Khanates became Islamic states. In many instances, Mongols assimilated into various Muslim Iranian or Turkic peoples (for instance, one of the greatest Muslim astronomers of the 15th century, Ulugh Beg, was a grandson of Timur). By the time the Ottoman Empire rose from the ashes, the Golden Age is considered to have come to an end.
According to the traditional view of Islamic civilization, which had at the outset been creative and dynamic in dealing with issues, it began to struggle to respond to the challenges and rapid changes it faced from the 12th century onwards, towards the end of the Abbassid rule; despite a brief respite with the new Ottoman rule, the decline apparently continued until its eventual collapse and subsequent stagnation in the 20th century. Some scholars such as M. I. Sanduk believe that the declination began from around the 11th century and still continued after this. Some other scholars have come to question the traditional picture of decline, pointing to a continuing and creative scientific tradition through to the 15th and 16th centuries, with the works of Ibn al-Shatir, Ulugh Beg, Ali Kuşçu, al-Birjandi and Taqi al-Din considered noteworthy examples. This was also the case for other fields, such as medicine, notably the works of Ibn al-Nafis, Mansur ibn Ilyas and Şerafeddin Sabuncuoğlu; mathematics, notably the works of al-Kashi and al-Qalasadi; philosophy, notably Mulla Sadra’stranscendent theosophy; and the social sciences, notably Ibn Khaldun’s Muqaddimah (1370), which itself points out that though science was declining in Iraq, Al-Andalus andMaghreb, it continued to flourish in Persia, Syria and Egypt during his time. Nevertheless, many agree that there was still a decline in scientific activity after the 16th
Despite a number of attempts by many writers, historical and modern, none seem to agree on the causes of decline. The main views on the causes of decline comprise the following: political mismanagement after the early Caliphs (10th century onwards), foreign involvement by invading forces and colonial powers (11th century Crusades, 13th century Mongol Empire, 15th century Reconquista, 19th century European colonial empires), and the disruption to the cycle of equity based on Ibn Khaldun’s famous model of Asabiyyah (the rise and fall of civilizations) which points to the decline being mainly due to political and economic factors.
North Africa’s Islamic civilization collapsed after exhausting its resources in internal fighting and suffering devastation from the invasion of the Arab Bedouin tribes of Banu Sulaymand Banu Hilal. The Black Death ravaged much of the Islamic world in the mid-14th century. Plague epidemics kept returning to the Islamic world up to the 19th century. There was apparently an increasing lack of tolerance of intellectual debate and freedom of thought, with some seminaries systematically forbidding speculative metaphysics, while polemicdebates in this field appear to have been abandoned after the 14th century. A significant intellectual shift in Islamic philosophy is perhaps demonstrated by al-Ghazali’s late 11th century polemic work The Incoherence of the Philosophers, which lambasted metaphysical philosophy in favor of the primacy of Revelation, and was later criticized in The Incoherence of the Incoherence by Averroes. Institutions of science comprising Islamic universities, libraries (including the House of Wisdom), observatories, and hospitals, were later destroyed by foreign invaders like the Crusaders and particularly the Mongols, and were rarely promoted again in the devastated regions. Not only was not new publishing equipment accepted but also wide illiteracy overwhelmed the devastated lands, especially in Mesopotamia. Meanwhile in Persia, due to the Mongol invasions and the plague, the average life expectancy of the scholarly class in Persia had declined from 72 years in 1209 to 57 years by 1242. American economist Timur Kuran has argued that economic development in the Middle East lagged behind that of the West in modern times due to the limitations of Islamic partnership law and inheritance law. These laws restricted the growth of Middle Eastern enterprises, and prevented the development of corporate forms.