Like any other civilization in human history, the Islamic civilization was prone to both internal and external threats. The factors responsible for the decline of Muslim power and prosperity include:
In 968, the low level of the Nile caused a terrible famine which resulted in the death of about 600,000 people. (The northern section of the river flows almost entirely through desert, from Sudan into Egypt, a country whose civilization has depended on the river since ancient times. Most of the population and cities of Egypt lie along those parts of the Nile valley, and nearly all the cultural and historical sites of Ancient Egypt are found along riverbanks). Similar famines followed. One terrible famine, which was caused also by a low level of the Nile, lasted seven years between 1066 and 1072. Peasants deserted their villages and agricultural production was diminished severely. These famines heralded the beginning of a series of natural disasters which resulted in the depopulation of Egypt. However, the greatest catastrophe in the Middle Ages was the plague of 1347, 1348 and 1349, which was known in Europe as the Black Death and which swept across the Islamic world and Europe. Thousands died every day, and the population of Egypt, Syria and Iraq was diminished by one third. These recurring famines and plagues were instrumental in diminishing agricultural production. Death wiped out a large proportion of peasants and domestic animals. Industry collapsed with the deaths of great numbers of skilled workers. This also had adverse effects on the administration and the government.
These were a series of religious expeditionary wars blessed by the Pope and the Catholic Church, with the stated goal of restoring Christian access to the holy places in and near Jerusalem. Between 1096 and their final defeat in 1291 no fewer than seven Crusades were mounted against the Arab lands. The first three (1096, 1147, 1189) focused on Syria, including Palestine. The Fourth Crusade (1204) pillaged Constantinople, while the Fifth, Sixth and Seventh Crusades (1218, 1244, 1250) were directed against Egypt. The last one (1270) was directed against Tunisia. During the conquest, the Muslim population of the captured Syrian towns was annihilated by mass slaughter, and was replaced by the members of the invading armies and those who accompanied them, such as adventurers, merchants and pilgrims.
The efforts to confront and oust the Crusaders, which lasted for two centuries, sapped the local economies and weakened the Arab urban centres. This enormous task required formidable military strength which could not be provided by Syria alone, with its limited human and economic resources. It was only through the unity of Syria and Egypt under the Ayyubids and the Mamelukes, and through the military system that was adopted, that the Crusaders were finally defeated and expelled.
The Ayyubid dynasty was of Kurdish origin founded by Saladin and centered in Egypt. The dynasty ruled much of the Middle East during the 12th and 13th centuries. Mamelukes on the other hand were originally slaves of nomad Turks who distinguished themselves in the service of the caliphate and are often given positions of military responsibility. They have the natural strength of small, self-aware military elite. They speak their own Turkish language in addition to the Arabic of their official masters. When the opportunity presents itself, they usually attack and seize power. The height of Mameluke power began in 1250, when they took control of Egypt. This lasted until 1517.
In the middle of the 13th century, and while the core Islamic lands were still busy with the expulsion of the Crusaders, another terrible invasion came from the East. Genghis Khan united the nomadic tribes of Mongolia and launched a devastating assault against the Eastern Islamic lands. By 1220/1221 Samarkand, Bukhara and Khwarizm fell into their hands and were cruelly devastated. In 1221, they crossed the Oxus River and entered Persia. Genghis Khan died in 1227. In the middle of the century, a new plan to conquer all the lands of Islam as far as Egypt was entrusted to Hulagu, who marched with an army numbering 200,000 men according to some Arabic sources. In February 1258 Baghdad fell into their hands. The Abbasid caliph Al-Musta’sim was killed and the caliphate was abolished. This marked the end of a remarkable era in Islamic civilization.
The Mongols looted and then destroyed mosques, palaces, and hospitals. Grand buildings that had been the work of generations were burned to the ground. Even the libraries of Baghdad, including the House of Wisdom (a library and translation institute) were totally destroyed. The Mongols used the invaluable books to make a passage across Tigris River. Survivors said that the waters of the Tigris ran black with ink from the enormous quantities of books flung into the river and red from the blood of the scientists and philosophers killed.
The most disastrous effect of the Mongol invasion was depopulation. The capture of Baghdad and several towns was followed by horrible massacres. The number of inhabitants who were slaughtered in Baghdad after its conquest according to Arabic sources ranged between 800,000 and 2 million; non-Arabic sources give lower figures. For example, Wikipedia encyclopedia cites “between 100,000 to 1 million.”
The decrease of the population of Iraq and the consequences of the Mongol conquest were so catastrophic that Hamd Allah al-Qazwini observed that, “there can be no doubt that even if for 1,000 years to come no evil befall the country, yet it will not be possible completely to repair the damage and bring back the land to the state in which it was formerly.” Modern research has revealed that the population of the province of Diyala, including Baghdad, had declined from 870,000 in the year 800 to 60,000 after 1258.
Immediately after the fall of Baghdad, the Mongols continued their march and overtook Syria and according to their plan, they were heading towards Egypt which was threatened also with annihilation and destruction. The Mamelukes realized the enormity of this danger, and they stood up to the challenge. In the battle of ‘Ayn Jalut in Palestine, in 1259, the Mongols were defeated decisively, and their tide was checked.