One of the great ironies of the current battle for Iraq is that for all the billions spent on the war on terror, all the bullets fired, all the lives lost, what may ultimately defeat al-Qaeda isn’t the United States or another Western power — but a group from within the jihadist movement. It didn’t take drones. Or the surge. It took a charismatic, emergent leader known as Abu Bakr al-Baghdadi, who recently threw off the yoke of al-Qaeda’s command and decided he and his militant pals would do their own thing.

They would become the Islamic State of Iraq and Syria, which on Sunday declared the restoration of the 7th-century Islamic caliphate. Baghdadi, anointed caliph, would rule over its vast tracts of captured territory in northern Iraq and Syria, the message said. And all Muslims worldwide must now pledge allegiance to him.

For a group long on guns and cash and defined by acts of audacity and ambition, Sunday’s declaration was perhaps its boldest move yet. It has announced something no other modern jihadist movement has done before — though some have wanted to — and showed its intention to destroy al-Qaeda. “This is a threat to the legitimacy of al-Qaeda as the representative of global jihad, and it lays down the threat big time,” Charles Lister of Qatar’s Brookings Doha Center, told The Washington Post’s Liz Sly. “Put simply, Abu Bakr al-Baghdadi has declared war on al-Qaeda.”

The ideological and recruiting power of al-Qaeda remains grounded in the mythology of the attacks of Sept. 11, 2001. But that power weakens the older those attacks become, analysts say. Today’s young foreign recruits, for whom jihadist groups compete and who are essential to the continuance of any insurgency, aren’t bound by that lineage. “Al-Qaeda’s greatest achievement was the 9/11 attacks, but that was 13 years ago,” wrote Haverford associate professor Barak Mendelsohn in Foreign Affairs. “Many of today’s jihadis were young children at the time” and don’t have much loyalty to the aging movement.

As such, analysts warn against underestimating Sunday’s declaration. “ISIS now see themselves as the legitimate leaders of the movement, and they expect everyone to fall in line,” Peter Neumann, who studies radicalization at King’s College London, explained to the Guardian. “For ideological jihadists, the caliphate is the ultimate aim, and ISIS — in their eyes — have come closer to realizing that vision than anyone else…. This could be the end of al-Qaeda…. This could mark the end of Bin Laden’s vision and his legacy.”

That end, if it comes to pass — and there are reasons it may not — has roots deep in the past.

The jihadist leaders of Iraq and those of Osama bin Laden’s al-Qaeda have long had differences, according to a study by the Washington Institute for Near East Policy. It begins with the divergent socioeconomic backgrounds between bin Laden and the murderous, Jordan-born Abu Musab al-Zarqawi, who led Iraq’s al-Qaeda before he died in a U.S. airstrike in 2006. Bin Laden was educated, urbane and upper middle-class. Zarqawi, meanwhile, had a criminal past and was poorer and less-educated.

“During the Iraq war, Zarqawi’s brash personality and belief that authority is derived from those on battlefield front lines rather than behind the scenes would create even more tensions,” wrote Aaron Zelin in the report. “Zarqawi became a household name for his brutal personal beheadings and fast-paced suicide bombing…. As a result, many foreign fighters wanted to join.”

This challenged bin Laden, who wanted to “own” the Iraqi jihad. But then, when it seemed as though they’d split, Zarqawi relented and pledged fealty to bin Laden in 2004.

ISIS leader Baghdadi, who assumed control of al-Qaeda in Iraq in 2010, appears to be an amalgamation of those two jihadist leaders. He’s reportedly a well-educated man but is also a battlefield tactician who’s willing to order such shocking acts of brutality that foreign fighters, including thousands from the West, have flooded his ranks. Baghdadi, who chafed under al-Qaeda leadership, wouldn’t be as conciliatory as Zarqawi.

In the winter of this year, after Baghdadi publicly said he “choose the rule of God” over the rule of al-Qaeda leader Ayman al-Zawahiri, the insurgencies split. “In addition to killing one another on the battlefield … it is likely that social media, especially Twitter, has amplified mutual hatred,” according to the Washington Institute.

But more than social media, what has hurt al-Qaeda has been ISIS’s recent territorial gains. Those successes have attracted fresh recruits and, analysts say, made al-Qaeda under Zawahiri appear weak, diffident and indecisive. “Al-Qaeda has maintained a slim but diminishing lead over ISIS among key key influencers in the movement,” wrote expert J.M. Berger, who runs the Web site IntelWire.

He said it also appeared to hurt al-Qaeda’s fundraising. Sunday’s “proclamation will likely generate new streams of fundraising and fighter recruitment” to ISIS, he wrote.

The power of an insurgency is in its currency. And today, the Washington Institute for Near East Policy said, al-Qaeda is a declining power. “It is too early to know, but if current trends hold, ISIS has opened up a lead on al-Qaeda, which has a steep hill to climb just to stave off its own relative decline.”