Not that al-Qaeda is ever a stabilizing influence anywhere that they turn up, but their ever-growing involvement in the ongoing Syrian Civil War is making both the war and any future peace agreement dramatically more difficult.
The efforts at orchestrating international peace talks are where al-Qaeda’s influence is really standing out. Since they amount to a huge chunk of the rebellion on the ground, and they’re not invited to the talks, it isn’t clear to anyone how a deal could even theoretically be reached to end the war.
Western officials are coupling this with some serious sour grapes about their own relatively feckless allies in the rebellion, accusing al-Qaeda of strengthening Assad by fighting with the pro-West rebel factions and by making the rebellion look like a bunch of jihadists.
But al-Qaeda is no small player in the war, and that means in practice the rebels really are, in large measure, a bunch of jihadists. Likewise, while the Western assumption seems to be that without al-Qaeda, the “moderate” rebels would be in a better negotiating position, the fact of the matter is al-Qaeda is the one doing most of the heavy lifting on the ground, and the Syrian military might well have already routed the rebels if it weren’t for the huge, ongoing influx of foreign Islamist fighters under al-Qaeda’s banner.
This is a lose-lose situation for ending the war, however, because al-Qaeda is unlikely to ever come to the table to negotiate a settlement, and a ceasefire that doesn’t include their fighters is no ceasefire at all.