The Islamic State, formerly known as ISIS (the Islamic State of Iraq and Syria), has become a bitter rival of al-Qaeda, its parent organization. Its leaders represent a new generation of Islamist militants who have broken with al-Qaeda in a power struggle over Syria and the future of the global Islamist revolution.

Both groups share the same ultimate goal: the establishment of a global caliphate, to be ruled under a harsh brand of sharia (Islamic law). But they clash over what strategy and tactics are best, as well as who should lead the global jihad (holy war) to build the caliphate.

Al-Qaeda today is a far different organization than it was during Osama bin Laden’s heyday. The network is more decentralized and far-flung. Its expansion was fueled, in part, by absorbing other Sunni Islamist extremist groups.

One of these groups was led by Abu Musab al-Zarqawi, a Palestinian Islamist extremist born in Jordan—one of the estimated 25,000 foreign Muslims who flocked to Afghanistan after the 1979 Soviet invasion to fight the Soviet and Afghan communists. Zarqawi was a close associate of Osama bin Laden, although he did not formally join al-Qaeda until 2004 when he was recognized as the leader of al-Qaeda in Iraq.

Zarqawi was killed in a U.S. airstrike in 2006. Subsequently, his organization was decimated by a U.S.-led counterterrorism campaign after many Sunni Iraqis revolted against its brutal tactics. But the group made a comeback in Iraq after the withdrawal of U.S. troops in 2011. The absence of U.S. troops took the pressure off the organization. Meanwhile, Iraqi Prime Minister Nouri al-Maliki’s Shia-dominated government alienated Sunni Iraqis, driving many of them to see ISIS as the lesser evil.

The 2011 outbreak of civil war in Syria presented al-Qaeda in Iraq with an opportunity to fill a vacuum in a failed state.  It expanded operations into Syria, rebranding itself as ISIS.  It proclaimed itself to be the champion of Syria’s Sunni Arab majority against the Assad regime, a secular dictatorship which was dominated by the minority Alawite sect.

The ultra-ambitious leader of ISIS, Abu Bakr al-Baghdadi, is an Iraqi who professes to have more religious credentials than previous al-Qaeda leaders.  He claims to be a descendant of the prophet Muhammad and has proclaimed himself as Caliph (successor) of Muhammad.  He also sees himself as the true successor of Osama bin Laden and has bristled at attempts by bin Laden’s chief lieutenant, Ayman al-Zawahiri, to assert leadership over ISIS.

The expansion of ISIS into Syria sparked friction with al-Qaeda’s official franchise in Syria, Jabhat Al-Nusra (the Victory Front).  In April 2013, ISIS leader Baghdadi unilaterally proclaimed a merger with Al-Nusra, which was led by one of his former lieutenants.  But Al-Nusra rejected the merger, supported by Zawahiri.

The rivalry over leadership of the Islamist revolution in Syria has led to violent clashes between the two groups. These internecine battles have left thousands of militants dead.

In February 2014, al-Qaeda disowned ISIS. It fears that Baghdadi’s extremely ruthless and brutal tactics will tarnish its brand and alienate many Muslims.

ISIS, for its part, claims that al-Qaeda has deviated from bin Laden’s path.  And ISIS enjoys several important advantages over the Al Qaeda core group led by Zawahiri.

While Zawahiri is hiding—supposedly in the remote tribal badlands along the Afghanistan-Pakistan border—ISIS controls territory the size of Maryland in the heart of the Arab Middle East.  This has given it access to oil resources and war booty—spoils that have made it the richest terrorist group in history.

The increasingly sectarian nature of the civil wars in Iraq and Syria also has been a recruitment boon to ISIS, helping it attract Sunni militants from many Arab countries, Europe, Asia and the West.  The younger generation of Islamist militants finds the mysterious ISIS leader Baghdadi far more appealing than the dour and elderly Zawahiri.  And ISIS cleverly amplifies Baghdadi’s appeal with a sophisticated propaganda apparatus that spews slick videos on multiple social media platforms favored by young Muslims.

This has enabled ISIS to recruit the lion’s share of the estimated 15,000 foreign fighters who have flocked to Syria and Iraq.  Al-Qaeda, which emerged from the war in Afghanistan against the Soviets, has established its own pipeline to exploit the war in Syria to funnel foreign fighters to its Al-Nusra franchise.  It also has deployed a cadre of veteran operatives, dubbed the Khorasan group by U.S. officials, which seeks to recruit foreign fighters in Syria for terrorist operations in their home countries.

The bottom line is that Al-Qaeda and ISIS increasingly are competing for recruits, funding and leadership of the global Islamist revolution.

The good news is that this power struggle may weaken both of them.

The bad news is that their rivalry may spark a competition to see who can launch the most spectacular terrorist attacks against Western targets.  Moreover, Syria has emerged as a terrorist sanctuary that potentially poses a greater threat to the United States than Afghanistan did before 9/11.