These changes were instigated by the mistrustful disposition of the caliph, who saw in every man a traitor and conspirator, dismissing on the slightest provocation his most devoted adherents, some of whom were even put to death by his orders.  His last choice, Yazid ibn Hatim, governed Egypt for eight years, and the caliph bestowed the title of Prince of Egypt (Emir Misri) upon him, which title was also borne by his successors.

These continual changes in the government of Egypt had not furthered the prosperity and well-being of the inhabitants.  Each ruler, certain of speedy dismissal, busied himself with his personal affairs to the detriment of the country, anxious only to amass by every possible means sufficient money to compensate him for his inevitable deposition.  Moreover, each governor increased the taxation levied by his predecessor.  Such was the greed and rapacity of these governors that every industry was continually subjected to increased taxation; the working bricklayer, the vender of vegetables, the camel-driver, the gravedigger, all callings, even that of mendicant, were taxed, and the lower classes were reduced to eating dog’s flesh and human remains.  At the moment when Egypt, unable to support such oppression longer, was on the verge of insurrection, the welcome tidings of the death of El-Mansur arrived.

Muhammed el-Mahdi, son of El-Mansur, succeeded his father and was the third caliph of the house of Abbas.  He was at Baghdad when his father expired near Mecca, but, despite his absence, was immediately proclaimed caliph.  El-Mahdi betrayed in his deeds that same fickleness which had signalised the caliphate of his father, El-Mansur.  He appointed a different governor of Egypt nearly every year.  These many changes resulted probably from the political views held by the caliph, or perhaps he already perceived the tendency shown by each of his provinces to separate itself from the centre of Islamism.  Perhaps also he already foresaw those divisions which destroyed the empire about half a century later.  Thus his prudence sought, in allowing but a short period of power to each governor, to prevent their strengthening themselves sufficiently in their provinces to become independent.

Egypt remained calm and subdued under these constant changes of government.  Syria and the neighbouring provinces followed suit, and the Caliph el-Mahdi profited by this peaceful state of things to attack the Emperor of the Greeks.  His second son, Harun, undertook the continuation of this war, and the young prince displayed such talent and bravery that he gained brilliant victories, and returned to Baghdad after having captured several cities from the Greeks, overthrown their generals, and forced Constantinople to pay an annual tribute of seventy thousand dinars (about $180,000).  The Caliph el-Mahdi rewarded Harun by solemnly naming him the future successor of his eldest son, Musa el-Hadi, whom he had just definitely declared his heir to the throne.  Shortly after this decision, el-Mahdi died, in the year 785, having reigned ten years and two months.