On Wednesday, it was reported that members of Jabhat al-Nusra, the Syrian arm of al-Qaida, had issued a loyalty pledge to a commander from the Islamic State of Iraq and Syria (ISIS) at a remote point on the Iraqi border.

The Syrian Observatory for Human Rights, the opposition-backed monitoring group that first reported the news, said that the merger is significant, paving the way for ISIS to take control of both sides of the border at Albu Kamal, in Syria, and al-Qaim, in Iraq.

If true, it could signal that ISIS – now in control of Mosul, Tikrit and most Syrian border posts – has begun to gain the tentative support of its arch rival and other extremist groups impressed by its newfound power following its success this month in Iraq.

But as ISIS prepares to attempt to push further into eastern Syria, Jabhat al Nusra – with the backing of the world’s largest terror organization, al-Qaida – remains a formidable opponent.

We asked Rania Abouzeid, a journalist who writes about Syria’s extremists and fellow at the European Council on Foreign Relations, Noah Bonsey, senior Syria analyst with the International Crisis Group, and Aram Nerguizian, senior fellow at the Center for Strategic and International Studies, to weigh in on the potential for further collaboration between the two, their relative strengths and weaknesses, and whether ISIS will be able to bring Jabhat al-Nusra and other factions under its umbrella – creating one cohesive unit.

Syria Deeply: Jabhat al-Nusra’s main goal is to unseat the regime. ISIS’s goal is to create a caliphate. How do we account for agreements like the one we saw this week near the Iraqi border?

Aram Nerguizian: You’re going to see [these] groups [alternately] compete, accommodate each other, and then return to competition. Let’s not forget that their roots are not dissimilar. These are organizations that basically have, fundamentally, the same ethos and ideas of how to go about what they want to do, about resource management and recruitment. So there is a space where they see eye to eye.

But they are distinct groups. They’ve built up separate strengths. There’s bad blood between them, although that doesn’t stop parties in any civil war from coordinating with each other. It’s too early in the game to say that one faction [has the ability] to steamroll another. It’s more a matter of who can shape the broadest mix of alliances with other groups, and create some sort of central structure.

Nusra doesn’t share the objectives of ISIS. But they are both jihadi groups, and they are both looking to create new realities on the ground. [Neither] fits the mold of the “weekend warrior” who got tired of the Assad regime and joined the militia or a fighting company in a local town or city. Maybe Nusra has expectations of what it can do that are far more localized within Syria, but the fact that they have ambitions in places like Lebanon [shows that] none of these groups are bound by geographic parameters.

Noah Bonsey: As for what we’ve seen recently in Abu Kamel, it’s not as if ISIS won the hearts and minds of the individuals from al-Nusra who pledged allegiance. As ISIS took control of nearby Iraqi territory on the other side of the border, it amassed military power in the area to a level where it likely became clear to anti-ISIS rebels in Abu Kamel that they would not be able to hold out much longer. The fact that some al-Nusra members are pledging allegiance to ISIS there is the result of the local balance of power on the ground. It’s a pragmatic decision.

Syria Deeply: How successful could ISIS be in drawing fighters from Jabhat al-Nusra and other militant groups?

Rania Abouzeid: The battlefield on the rebel side has always had an element of fluidity, in terms of men switching battalions as individuals or as a group, pledging allegiance to a larger or more successful or well-funded unit or coalition.

ISIS has been drawing fighters away from al-Nusra and vice versa since ISIS was announced in April 2013. Some have opted to fight under Nusra’s banner, heeding the words of al-Qaida chief Ayman al-Zawahiri who has disavowed ISIS and challenged its actions. Others have followed ISIS leader Abu Bakr al-Baghdadi and see him as the pre-eminent global Jihadi leader, a man who unlike Zawahiri, is on the ground in the newest battlefields in the heart of the Arab world.

As Baghdadi’s Islamic state increasingly takes shape and the group not only extends its influence in parts of Syria and Iraq, but also holds that territory, it may yet draw more men from both Nusra and other Islamist battalions who ultimately want to see an Islamic state and may feel that ISIS is the best group to make that happen.

Noah Bonsey: In Syria, the cost for ISIS of territorial expansion is high, much higher than it currently is in Iraq. That’s primarily because of the depth and breadth of anti-ISIS sentiment inside Syria, including among fellow jihadis and leading rebel groups. So ISIS’s problem is much bigger than al-Nusra – they are also hated by just about everyone in the opposition.

Syria Deeply: What chance does it really stand of making itself the sole extremist act in Iraq and Syria, and what would they need in order to make that happen?

Abouzeid: I don’t think ISIS will be the sole ultraconservative player in Iraq and Syria. This is a battlefield populated by many players who represent groups across the Islamist spectrum and outside it. Despite the vicious inter-Jihadi feud between al-Qaida and ISIS, al-Qaida will not easily cede its foothold in this area. The bad blood between these two groups is substantial, and unless they reconcile, they are likely to both remain players, to greater or lesser degrees.

Bonsey: ISIS has slowly but steadily been gaining ground in Deir Ezzor for weeks now, even before the surge in Iraq. The surge strengthens ISIS’s hand further, but it’s still going to have to fight for the territory it wants, against both al-Nusra and the broad spectrum of non-jihadi rebels. You’re unlikely to see many fighters changing sides and joining ISIS until they have no other choice.

Syria Deeply: How strong is Jabhat al-Nusra right now in Deir Ezzor?

Bonsey: In Deir Ezzor, Jabhat al-Nusra has combined its resources with most of the main rebel actors in an alliance known as Majles Shura al-Mujahideen. Together, these forces are fighting ISIS. Thus the question in Deir Ezzor is not how strong al-Nusra is, but how strong are all the anti-ISIS militants combined?

The answer is that they’re quite strong, and until recently the fight had been relatively even. But ISIS has two main advantages. One: even before its Iraqi surge, ISIS was steadily gaining ground in Deir Ezzor, because that is where it has focused its main combat resources in Syria. ISIS pulled back months ago from the main fronts with the regime in the north, and it has focused on seizing control of Deir Ezzor rather than seeking to gain significant ground elsewhere in the country. In contrast, al-Nusra and leading rebel factions fight ISIS in Deir while continuing to bear the burden of battles with the regime in Aleppo and throughout the north.

ISIS’s second advantage comes from all the money and weaponry it has gained from its Iraq surge. This strengthens the group and provides it with additional resources for the fight in Syria. We can say now that ISIS appears to have the upper hand in Deir Ezzor – but the fight remains a tough one.

Syria Deeply: What happens next for ISIS in Syria and Iraq?

Nerguizian: The question is, How will ISIS evolve, adapt and potentially survive over the coming weeks and months? If you’re in another jihadi group right now, you’re waiting for the other shoe to drop in terms of what will be the response of the Iraqi Shia militias, even the conventional Iraqi armed forces – and then what will be the counterterrorism response from countries like the U.S. and Gulf countries? There’s a lot hanging in the balance. I think ISIS is done patting itself on the back, in terms of having made this massive incursion to Iraq in force, and the question is: What can they hold? How can they create governance structures that don’t completely chafe against the social fabric of these towns?