Not to pick on you specifically, but there have been a lot of this sort of a question recently.

This is not a well-phrased question.

If you want really good answers from good historians, you need to frame your question positively, ie. "Why did X happen?" Asking why something didn't happen can only generate vague answers at best, as it runs into the post hoc problem even harder than usual empirical study.

Historians do not know what outcome events that did not happen would have had. This, beyond all else, is the most obvious lesson taught by deep historical study.

So, try to look at it in a more positive sense: Why did the predominantly Muslim areas of Africa and the Middle East form into the states, societies, and cultures they did? This question, though complicated, might actually have a valid answer.

You're holding them to unreasonable standards. There are countless other examples of large and successful empires in the past whose territory today also is - how to put it? - troubled.

Central America rivaled anything in the Middle East in its day, Southeast Asia was once largely unified and home to prosperous regional powers, sub-saharan Africa had the Mali empire, etc.

So to ask why the Middle East was once more successful/powerful than it is now without acknowledging that theirs is a common trajectory is to ignore the history of most of the world.

To get to a real answer, I would say the biggest factor (perhaps in every case listed above) was the preeminence of Western European power at the dawn of the global era. Modern conflicts in places like Syria, Iraq, Libya, and Egypt can be directly linked to a history of Western involvement from the colonial period right up to the modern day. Exploitative economics, governmental mismanagement, and the extremism bred by oppositional identity have all contributed to political instability.

It may be inappropriate, but I like to draw analogy to the situations in Anatolia, the Pontic regions, and the Levant in the period of Roman imperial dominance. It's rare for any people to be subject to foreign intervention and not take a while to recover.

On the other hand, don't ignore that many of the nations of the Middle East ARE doing quite well for themselves!

Are you defining these empires' "glory" relative to their neighbors, or against some absolute standard of prosperity and power?

Italy has never reclaimed anything close to what the Roman Empire held. France hasn't reclaimed what it had under Napoleon. England once ruled a quarter of the world's population. Spain has lost sprawling New World holdings and unimaginable wealth.

Now, most of those countries are still rich and relatively powerful, but none of them are in any sense "back to their former glory".

Unless you define glory in terms of wealth and creature comforts, in which case almost every part of the world (including the Middle East) is better off than it was in its "golden age."

As a lot of other posters have said here, there are a lot of incorrect assumptions to your question.

Those aside, however, I'll venture a crack at it.

There were of course great Muslim empires - The Rashidun, Umayyad and Abbasid caliphates dominated the modern Middle East and beyond, stretching from Spain to India and attaining technological and scientific prowess that eclipsed Europe of the time. In the 1200s, however, the Muslim world faced repeated waves of invaders - Repeated Mongol and Timurid invasions killed millions, razed dozens of cities (including Baghdad, the heart of the Muslim world at the time), and forever ended the era of multinational Arab empires.

With receding Mongol power, however, the rise of the Ottoman Turks (especially after their conquest of Constantinople in 1453) brought a new unifying force to the region, eventually uniting most the of the former Caliphate territories (the Ottoman Sultans claimed the title of "Caliph" for themselves, though more for ceremonial/liturgical purposes than any serious attempt to emulate the former Caliphates (cf. Holy "Roman Emperors")). From the 15th until the 18th century the Ottoman Empire was arguably the most powerful polity in the world (with the possible exception of China), at its height controlling everything between Vienna (which it sieged twice but never captured) and the Persian Gulf, and it subsequent domination of land and sea trade routes through the region brought it fabulous wealth and grandeur.

However, the Ottoman Empire never had access to the resource that would bring about its downfall: transoceanic colonial empires. As Britain, France and the Netherlands especially began establishing footholds in the Indian ocean and East Asia, the writing on the walls became clearer. The Ottoman Empire's vital trade positioning at the crossroads of East and West was simply being sailed-around. Throughout the 19th Century the empire went into steady decline, being known as the "Sick Man of Europe", and one by one its far-flung territories gained effective or complete independence.

The final nail in the coffin, of course, was the First World War, after which the Empire ended and Britain and France carved up its many regions into mandates and protectorates, causing the same problems we see in Africa: borders were drawn with little regard for ethnic, religious, or linguistic lines, creating problems such as the Kurds being divided between several different countries, or Iraq lumping together 3 major ethno-religious groups.

Since then a few major factors have dominated the Middle East: first, the Israel/Palestine question which is easily combined with Cold War politics has made the formation of a large Unified Muslim state impossible - Turkey and the Shah of Iran were backed by the US, and Saudi Arabia is usually in the US camp (except on questions of Israel/Palestine) whereas Egypt attempted to maintain Neutrality and the other Arab states were supported by the USSR. Second, the rise of Oil might seem like a source of power for a growing Muslim superstate (Saudi Arabia would qualify, to an extent), but as the Gulf War demonstrates Oil wealth can be a source of contention. Oil, especially in areas without other major industries, notoriously often causes economic decline except for an accumulation of wealth in the hands of the land owners/rulers (known as the "resource curse"). Third, the 1979 Iranian Revolution brought reactionary and aggressive Shi'a rulers to power in Iran, causing massive instability in the region (see Iran/Iraq war and Iranian support of Hezbollah).

TL;DR - The Muslim world has only had 95 years since its last great empire, cut them a little slack!

Sources

Genghis Khan and the Making of the Modern World - Jack Weatherford

A History of the Arab Peoples - Albert Hourani

In one word: Colonialism. In an extra, hyphenated word: Neo-Colonialism

However, that's not really enough of an explanation considering former colonies in Asia have recently been "prosperous," and by that I mean an increase in GDP, but not necessarily an improvement for large portions of society. India is a typical "success" story, but has people without access to drinking water living alongside millionaires driving Mercedes Benz's through the streets. I wouldn't necessarily say they're glorious inspirations for today's Third World, but I digress. That's another conversation for another day.

There's a common myth that Africa (as a hole) is bereft of natural resources except oil and fruit. The reality is quite different.

In terms of natural resources, Africa is the world's richest continent. It has 50 percent of the world's gold, most of the world's diamonds and chromium, 90 percent of the cobalt, 40 percent of the world's potential hydroelectric power, 65 percent of the manganese, millions of acres of untilled farmland as well as other natural resources. Source

All these riches made it especially hard for Western governments to let go of Africa. For hundreds of years Britain, France, Belgium, and, a bit later, the United States, treated Africa as their resource pool. Before colonialism started, they encouraged wars between the West African empires to secure more slaves for their slave-trade in the New World. Under Colonialism Africans saw their resources plundered while they received nothing in return. The only infrastructure the colonial governments bestowed onto Africans was one designed to quickly extract resources from the interior to the coast and schools that encouraged only a small percentage of the population to ignore their traditional heritage and independence, and instead to work for the colonial government. Only when it became too expensive to keep colonies and frowned upon by most of the world did the Western governments pull out of Africa. Decolonization was hard on Africa and the Middle East. No attention was paid to the indigenous populations. Ethnic tensions, languages, religions, traditional borders, who cares? The West carved their slices of the pie with their eyes on natural resources alone. In fact, huge portions of the continent had never even been seen by Westerners when they drew the borders. The Berlin Conference has truly been a massive hindrance in Africa's progression in the post-colonial era.

The past 50 years haven't helped. Neo-Colonialism's legacy will be encouraging Africans to focus their economy on producing cash-crops and extracting natural resources. Unlike South Korea, Japan, India and China, much of West Africa (and other parts of Africa) have been encouraged to remain unindustrialized. As a result, jobs are low-wage, uneducated labor in farming or extracting raw materials. Governments and large corporations (many who were working for the state) prefer to work with leaders whom are willing to take a bribe to allow multinationals to pillage resources with little benefit to the whole of the population. There's a devastating culture of corruption in West African politics where the vast resources of the countries are sold to foreign multinationals, by corrupt leaders who line their pockets while the rest of the population suffers.

Like others have said, It takes a while to shake the legacy of colonialism and Africa has a lot of special, extra-difficult cases.

Source: How Europe Underdeveloped Africa by Walter Rodney

Edit: A formatting uh-oh.

I did a lot of casual reading in Islamic history after 9/11, and I came away with the impression that, for reasons not clear in the text, larger Islamic states (with the possible exception of Indonesia) have never come up with a lasting answer to the question of how to govern a multi-ethnic, multi-confessional state, and that limits the maximum stable size of an Islamic state to the geographic area of a single tribe, most or all of whose members are of a single faith tradition, plus however much land they can physically dominate.

I counted at least three, and maybe five, times in Islamic history when "great caliphs" built empires by promising tribes, and in some cases faith traditions, other than their own equal and fair treatment if they would unite with the caliph's own tribe. Within at most three generations, the caliph's grandson or great-grandson was vulnerable to the (bad) advice from members of his own tribe or his own faith tradition: "why are you wasting resources on other tribes and other faiths when there are any members of your own faith and tribe who aren't rich yet?" That was, consistently, the caliph who, the first time the caliphate came under internal economic or external military pressure, saw huge defections to one or more enemies, and the caliphate fell apart. Only to be reconstituted later, with a new great caliph, in a different capital city, around the same promise of fair and equal treatment, only to fall apart the same way a few generations later, ad infinitum.

Of course, some of those economic or external pressures were predictable. The Ottoman Empire had very powerful, much larger, hostile neighbors. The Mughal Empire derived its vast wealth from taxing the Silk Road, which the great sea powers eventually learned to bypass. The Malian Empire declined for similar reasons when the land route between the gold coast of Africa and the Mediterranean declined in importance. But it seems to me that they could have responded to those pressures better if they hadn't disintegrated into internal tribal or sectarian squabbling over the declining revenues, or tribally or religiously motivated accusations of traitorous intent.

I know that, in the late colonial period, a lot of those tribal and sectarian conflicts were energized by, stirred up by, European colonial powers playing a rousing game of "let's you and him fight" -- but I also see historical accounts of great empires and great caliphates falling apart for the same reason long before the European powers mattered in those regions.

People who've studied this far more professionally and in far more detail than I have: is this a fair summary?

The Mongol Invasion literally set back the Islamic countries quite literally centuries worth of progress. The Great Library of Baghdad, the massacre upon massacre was horrific beyond all horrifics. It is arguable that one invasion alone on the [Siege of Baghdad](http://en.wikipedia.org/wiki/Siege_of_Baghdad_(1258%29) set back mankind as a race; the Mongols in general were responsible for the greatest single cause of loss of life by percentage of all humanity living on the planet, and arguably by absolute numbers if you consider both war and massacre, and indirect loss of life from sieges and disruption of food supplies.

At the time, (1200's) Baghdad was the jewel of sciences, math, philosophy, art, culture. Then the Mongols came. It is debatable but a possibility they would have done the same to Europe. In any case, what happened is that they set back both China and Islam and set the ground stage for what would be the European Renaissance. Western countries were indirectly helped in no small part due to Mongols stomping the lifeblood out of Islam.

In general, China and Islam were the two most advanced nations, with Europe in third. Then the Mongols came, is how I understand it.