“The Syrian government does this fairly often,” said Robert S. Ford, the former American ambassador to Syria. “They have moved a lot of rebel fighters through these truce agreements, into Idlib, for instance, or Deir al-Zour. They’re just kicking the can down the road, figuring there may be other ways to reduce Idlib or Deir al-Zour later.”

But deals between factions that are trying to kill one another depend not so much on good will as on a belief that keeping their word now will mean that future deals will be honored. It also assumes that the other side will have something to offer in the future.

The Islamic State faction, seemingly on its heels, held a weak hand. Mostly all it had to trade were some dead bodies.

When Lebanese Army and Hezbollah militiamen, along with the Syrian Army forces, surrounded them on the border near Arsal, Lebanon, they negotiated their freedom and safe passage to the town of Abu Kamal, on the eastern Syrian border with Iraq.

By the time the convoy was on the road across the Syrian desert toward Abu Kamal, the American Air Force had been alerted. “So we decided to go look for these buses and we found them,” said Lt. Gen. Stephen J. Townsend, the American coalition commander. “And so we watched, and when ISIS came out to link up with them, we started striking ISIS. And again, we haven’t struck the convoy, but we have struck every ISIS fighter and/or vehicle that has tried to approach that convoy, and will continue to do that.”

Even before the Americans struck though, the ISIS convoy ground to a halt, at a place called Humaimah, the last town before Deir al-Zour Province, and Islamic State territory. They were being escorted by Hezbollah, the Lebanese militia that is fighting for President Bashar al-Assad in Syria. Hezbollah is backed by Iran, which has both trainers and fighters in the country as well.