Why is this coup different from all other coups? Why are Egyptians still fighting and dying in the streets of Cairo?

Because the Muslim Brotherhood is not just another political organization; and because Egypt is not just another country.

The toppling of the Muslim Brotherhood government of Mohammed Morsi and the slow-motion civil war developing in its aftermath is likely even bigger news than we yet realize. The takedown of the Brotherhood in the land of its birth creates an existential crisis not only for its Egyptian supporters, but across the Islamist world.

The Brotherhood and the Islamist forces it has spawned are a uniquely triumphalist mix of religion and politics. They are supremely confident in the correctness of their theo-totalitarianism, geopolitical vision, and ultimate victory in a way difficult to appreciate from the relativist Western perspective.

In no Western country could a major religious group matter-of-factly vow to "kill all Jews" or routinely torch churches. No Western politician could, like Morsi himself, urge his people to "nurse our children" on hatred for Jews, a.k.a. "bloodsuckers" and "sons of apes and pigs."

In contrast to the often ambiguous worldviews of the West, Islamists have a comprehensive set of fundamentalist beliefs -- to them, knowledge -- encompassing all of life's answers. They offer their followers social structure and community, purpose and mission, and certainty that they are always correct in any dispute with nonbelievers. Their House of Islam is in a collective, perpetual struggle against the rest of the broadly-defined infidel world and forces of evil, which often includes more moderate strains of Islam. They are energized by their march toward inevitable victory of their true faith over that of the infidels.

Such a triumphalist religion, as Bernard Lewis has written, can be summed up by the creed: "I'm right. You're wrong. Go to Hell."

But Islamism is also distinguished by the degree to which its triumphs feed its triumphalism. What better proof is there of the truth of radical Islam than its success? What better evidence can there be of the rightness of the cause than the string of victories granted by Allah? What movement has been more successful over the past decades than the Muslim Brotherhood and related Islamist forces? That success is critical to its appeal. As that philosopher-statesman Osama bin Laden understood, "When people see a strong horse and a weak horse, by nature they will like the strong horse."

Success breeds success. It reinforces certitude. The strong horse is an unbeatable recruiting tool. Especially when that horse will trample those who won't climb on.

Throughout the Middle East, Islamist forces have gone from strength to strength over the past decades, with few setbacks. The Brotherhood created formidable movements in nearly every Muslim country. They formed shadow governments in the countries in which they operated, and were generally the most potent and powerful organization outside of the regime. Though operating just outside government scope, they could still strike at their rulers for betrayal of Islamist principles, such as their assassination of Egyptian president Anwar Sadat for making peace with Israel.

In recent years, they have flexed their political muscle and taken over various governments. And no prize was greater than Egypt -- taken over by popular election, no less.The most populous Arab country is also the most dominant in Arab politics. The Brotherhood was now governing on the main stage.

But, like many revolutionaries before them, the Muslim Brotherhood failed to govern any better than its predecessors. In fact, violence, poverty, persecution, repression, and economic decline marked their year in power. If this dystopia was a taste of the coming caliphate, many wanted no further part in it. Thus, the army takeover has enjoyed popular support even among many who voted the Brotherhood into power.

That failure is cataclysmic for a movement which feeds off its own success. Brotherhood forces may be as fierce as ever, but they are, evidently, not invincible. Nor is their ultimate victory any longer inevitable. That shattered sense of invincibility and inevitability poses a major problem for continued Islamist growth and popular support. The invincible strong horse just broke a leg.

Not coincidentally, challenges from within to Islamist power are now emerging. In Tunisia, the emboldened secular opposition has taken to the streets and forced the Islamist government to negotiate for a new government. In Gaza, where the Brotherhood grip seemed unbreakable, a Palestinian Tamarod ("Rebellion") movement has emerged, vowing to "reject death under Hamas's security club."

The Muslim Brotherhood is hardly a spent force -- and woe to its opponents if it emerges victorious. But as this unprecedented setback undermines its claim to divinely ordained power, its stock may have peaked.

The battles in the streets of Egypt are not about principles of liberal democracy. They are not about which autocratic government will govern more efficiently.

They are about the Muslim Brotherhood fighting for its life. Having won Egypt before, it cannot now afford to lose. If the Muslim Brotherhood is defeated in Egypt, Islamism will be shaken everywhere.

For triumphalist Islamists, defeat is religiously unthinkable. The strongest horse isn't supposed to retreat from its forward march.