From the Assyrians, to the Achaemenids, Alexander's Empire, Parthians, Sassanids, the Arab Empire, Ummayads, Abbasids, and various before, between, and since, the middle east has seemed to have been constantly dominated by various large empires until recent history? Is this pattern pure coincidence or are there factors and reasons which allow this to happen?
Hi!
I can only talk about the early Islamic period (up to the coming of the Seljuks), but there are probably some things we should clear up before moving on. I hope that some researchers on the Diadochoi period could also respond, because it's been a while since I looked at that myself.
How do we define the Middle-East? Within our field of study, there are differing opinions on what constitutes the Middle-East. For example, I'm currently living in Tunisia, which I would consider a part of the Middle-East, but other people may disagree with me, considering the Maghreb (Libya, Tunisia, Algeria, Morocco) a different region altogether. Some consider Egypt to be part of the Middle-East, but differing opinions would put the border at the Sinai. Those who would include Egypt might similarly not include the Horn of Africa. It seems that you seem to favour the notion of the Middle-East being Anatolia, the Levant, Mesopotamia, Greater Iran and the Arabian Peninsula. I would even go a bit further and say your definition of the Middle-East is restricted to Mesopotamia (modern-day parts of Syria, Iraq, and Kuwait).
At the risk of giving off a serious arm-chair governor vibe, Mesopotamia and Egypt are probably rather easy areas to control. They are for the most part flat, fertile, and cut off from immediate access: the Zagros mountains in the case of Mesopotamia and the Red Sea in the case of Egypt. Of course both areas are still vulnerable from the south and west, but we'll get to that too.
The Middle-East in the early Islamic period So I will now focus on my actual area of specialisation, which is the early Islamic period. Despite the image imprinted upon us of the 'Abbasid caliphate' being a unified structure, which had clearly defined borders, until the Mongol invasion and the subsequent raze of Baghdad in 1258.
This image is only partially true. Let's go back to the rise of the Abbasids as a state to explain what happened in detail. The Umayyads had been in power for almost a century when they were violently overthrown by the 'Abbasids. Half a century later, a political crisis at the beginning of the 9th century, resulting in the death of the Caliph al-’Amin shattered Mesopotamia and left the Abbasids internally weak, and it is almost immediately afterwards that the Caliphs became increasingly dependent on the protection of Turkic warlords, turning more into figureheads from whom (semi-)independent rulers drew legitimacy, but controlled little more territory outside the palace in Samarra.
As a result, many autonomous statelets sprung up all over the Mesopotamia and the Levant, and Egypt was completely lost from 868 onwards. It has been argued that one of the reasons for the initial response to the Crusades was so lackluster was that the various emirs were more concerned expanding outplaying their Muslim rivals than to pay attention to yet another political actor in the area.
tl;dr: the actual period during which the Middle-East was united under one Islamic 'empire' was rather short; particularly during the middle-Abbasid period many different statelets sprung up
References: Crone, P. "Post-colonialism in 10th century Islam" (2006) Hillenbrand, C. Islamic Perspectives on the Crusades (1999) Kennedy, H. The Prophet and the Age of the Caliphates. (2004)
If you want more exact references, like page numbers, I'll have to add them tomorrow (: It's past midnight in Tunis, so I should probably sleep.