My knowledge on the middle east historically is pretty limited, but I do have a basic understanding that it use to be home to some very advanced and very stable empires, what were the events leading up to what it is today (unstable, poor, etc etc).
The fragmentation of the Middle East really began in the time of the Abbasid Caliphs. The Abbasids ruled over such a vast stretch of land, that the fringes were always trying to pull away from Baghdad. The Abbasids accomplished a victory over Tang China in Central Asia, but by and large the edges of the empire were tearing away.
In Spain, the toppled Ummayads revived their dynasty. Iberia was never regained. In the further reaches of Arabia, tribal uprisings were a constant menace. In the steppes that were the northeastern frontier of the caliphate, nomadic incursions also threatened. Meanwhile, the Abbasid ruling class became ensconced in the magnificent new capital they had built, Baghdad.
In Destiny Disrupted by Tamim Ansary, it is noted the Mesopotamia has a kind of "defanging" effect on its conquerors. Since the dawn of civilisation, there's been a repeated pattern: war-like, nomadic invaders attack the city-dwellers of Mesopotamia. The invaders then become rulers of the cities, and, dwelling constantly in them, lose their aggresive edge, becoming just as passive as their subjects. Then a new invader comes along and repeats the process.
This is clearly on display with the Abbasids. The Caliphs in the first century after Mohammad campaigned vigorously, expanding their realm at break-neck speed. The Abbasids, however, moved the capital from Damascus in Syria, close to the frontier with the Romans, to the new city in Mesopotamia. They soon became enamoured with the pleasures of their capital, leaving it less and less frequently. This meant power devolved to local governors, who weren't always loyal to Baghdad. Persians, Berbers and others built up breakaway principalities that only nominally acknowledged the Caliphs rule. Eventually, in North Africa, a rival Shi'a dynasty, the Fatimids, sprung up, and soon Egypt, Palestine and even the two holy cities had fallen to them.
This is where the Turks enter the picture. As the Arabs lost their warrior edge, they began to rely more and more on mercenaries. The Turks, migrating from the north, were the perfect option. Soon, entire armies of the caliphs were composed of Turks and led by Turkish generals. They ensured the security of Baghdad, but their employment came at a price. Predictably, wherever they went, the Turks began to seize control for themselves.
Unlike, for instance, the Persians, who had strong traditions of centralised rule, the Turks were still a tribal people. At the start of the second millennium, the Seljuqs provided an overarching authority, but their great sultanate splintered quickly until, even in the heart of Mesopotamia, independent warlords reigned supreme as emirs and, a new title, sultans. All, of course, acknowledged the supremacy of Baghdad; but the caliphs were now merely figureheads. Even in their own vicinity they had lost most of their authority.
Thus begins the history of the fractured Middle East, no longer a unified, energetic empire, but a patchwork of scores of squabbling states. Now and then, an energetic ruler would rise up to pull together a greater area under his control, but his kingdom would quickly break apart after his death. The arrival, first, of the crusaders, then of the Mongols furthered the splintering process.
It's important to note, though, that under the Ottomans from the 15th century, the Middle East was, once again, "one of the most powerful and stable areas in the world". They succeeded where others had not, with a centralised bureaucracy and an efficient military apparatus. Nevertheless, history regresses to the norm, and even the Ottoman "Empire" had become vastly decentralised by the 18th century. Today, we tend to blame the Sykes-Picot agreement and Western powers in general for the irrational borders and fragmented situation of the Middle East - the Arab world in particular. What we forget is that this has been the Middle East's status quo for a far longer time than the West has been able to interfere in it, thanks to the failings of their rulers and the difficulties of geography.
Which century are we talking? Are we post-classical? 20th century?