HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR: Homs, Syria, is where the uprising against President Bashar al Assad began in 2011. Today, the first of thousands of opposition fighters and their families began evacuating the last rebel-held neighborhoods. They’re leaving as part of a deal brokered by Russia, which backs President Bashar al Assad.

As the Syrian civil war entered its seventh year this week, the American military presence is higher than ever before, with the Trump administration sending 400 more troops to join 500 already deployed.

For more perspective on what’s happening on the ground and the role of the U.S. military, I’m joined from Washington by Doug Ollivant of the New America Foundation.

Doug, half a million people dead, getting into seven years now, millions more displaced. Any end in sight?

DOUG OLLIVANT, NEW AMERICA FOUNDATION: Unfortunately, no. It doesn’t appear that we really do have an end in sight. We see talks of cease fires and talks of truces, and, you know, the occasional peace talk, but nothing seems to have come from this.

The Russians are very much vested in the survival of the Assad regime. So, that seems to be a simple fact on the ground. And yet the rebellion hasn’t gone away, and neither have either al-Qaeda or ISIS. It’s complicated.

HARI SREENIVASAN: And he has time on his side. He doesn’t seem to feel any pressure to try to resolve this any sooner than needed?

DOUG OLLIVANT: That’s absolutely right. He’s very secure in Damascus, so the battle may wax and wane out in the field, but he’s under no particular pressure where he is.

HARI SREENIVASAN: Let’s talk about this idea that the U.S. has kind of a plan to tackle ISIS in Iraq and other places, and also in Syria. What are all these additional troops going to do on the ground?

DOUG OLLIVANT: Well, the additional troops in Syria are there to about three things. They’re there to advise — as they’ve been doing on the Iraqi side of the border. They’re there to provide fire support. There are howitzers at the space which can reach Raqqah or at least the outskirts of Raqqah. That’s also something that’s been done in Iraq. So, that’s a proven model.

But unlike in Iraq, these troops are there, least in some part, to keep our allies from fighting each other. They’re essentially positioned between the Turkish-backed Arab forces and the Kurdish forces, both of which would probably much rather fight each other than fight ISIS

HARI SREENIVASAN: You know, taking a city like Raqqah is going to take quite some time, and what we’re seeing in Mosul play out, I’d imagine that it would be just as hard, if not harder in Raqqah.

DOUG OLLIVANT: It would be harder. Raqqah is a smaller city than Mosul. So, in that sense, it’s easier.

But in Iraq, we’re blessed with an abundance of real, organized allies. We have the Iraqi army and its associated forces. We have the Kurdish Peshmerga and we can even work with the private military forces, PMUs or Shia militias. So, we essentially have three organized forces in that country that we can use as a fighting force.

In Syria, we really don’t have any of those things. We do have the YPG Syrian Kurds, but that’s a force we essentially organized. It didn’t organize itself, as the Iraqi Peshmerga did. So, we have been essentially creating that from scratch over the last several years

HARI SREENIVASAN: How strong is al-Qaeda in Syria today?

DOUG OLLIVANT: Well, al-Qaeda has continued to gain strength. All the extremist factions — ISIS, al-Qaeda in Syria, which has gone through various names. Today, it’s called Tahrir al-Sham. But al-Qaeda in Syria is still just fine.

And for that matter, Ahrar al-Sham, which doesn’t intend to impose Islam on us. They’re not like al-Qaeda or ISIS in that sense, but they’re essentially the Syrian Taliban. They want a very Islamist regime in the country.

All three of these groups have essentially gobbled up the smaller groups. They have more resources and, therefore, the fighters have moved from the more moderate resistance groups to these more Islamist groups

HARI SREENIVASAN: Considering how many different factions are fighting inside Syria and the different agendas that all of them have, do the major players — say, for example, the U.S. and Russia — can they possibly agree on actually fighting ISIS and al-Qaeda, versus supporting or not supporting Assad?

DOUG OLLIVANT: It’s very, very difficult. Ultimately, getting rid of ISIS is everyone’s goal. It’s the American — not just the Americans and the Russians, but even, say, the Saudis and the Iranians, also major players in the region, and the Turks, would all like ISIS to go away. But there are other equities, and exactly how you want the chess board to look once ISIS is gone, on that, there’s no agreement between any of the major powers

HARI SREENIVASAN: And in the meantime, the humanitarian crisis continues.

DOUG OLLIVANT: Absolutely. As you said, half a million dead, tens of millions who have been dispersed, many of whom have, you know, drown in one of the oceans or have been picked up by human traffickers and subjected to various indignities or death. It’s a true humanitarian tragedy

HARI SREENIVASAN: And continuing to add pressure on all the countries neighboring Syria as well.

DOUG OLLIVANT: That’s right. In countries that don’t have much stability to begin with, places like our ally Jordan, like Lebanon, Turkey — they’ve all received literally millions of refugees, as has Europe, and none of this is helpful for anyone’s political situation, and in the case of the neighbors, even regime survival

HARI SREENIVASAN: All right. Doug Ollivant of the New America Foundation — thanks so much.

DOUG OLLIVANT: Pleasure, Hari.