MICHEL MARTIN, HOST:

We're going to stay with Syria for a few more minutes. This long war has claimed the lives of more than half a million people and displaced about half of Syria's population. It's being called one of the great tragedies of the century. But we wanted to take a step back now and look at how we got here and what's next. Andrew Tabler is with the Washington Institute for Near East Policy. He's author of "In The Lion's Den: An Eyewitness Account of Washington's Battle With Syria," and he's with us now from his home office in the Washington, D.C.-area. Mr. Tabler, thanks so much for speaking with us.

ANDREW TABLER: Pleasure to be with you.

MARTIN: So why is the fate of Aleppo considered to be such a turning point in the conflict? And do you think that it is?

TABLER: It is a turning point. Aleppo is Syria's largest city. The rebels had taken over half of it in the summer of 2012. And controlling a major city in Syria was very important for the rebellion. And their attempt to hold it these last few years became sort of the heart of the revolution in many ways, particularly in the western part of the country. And the taking of Aleppo by the regime is a major setback for the rebels, but it's not going to end the war.

MARTIN: It's not. Why not?

TABLER: Well, two-thirds of Syrian territory is outside of Bashar al-Assad's control. Most famously, we have the eastern part of Syria, which is controlled by ISIS, but many of the rebel groups control areas in the northwest, the south. In the northeast, the Kurds and also other Arab tribes control other areas. So Syria's still a fragmented country, and Bashar al-Assad simply just does not have the troops to rapidly retake all those areas. So while Aleppo fell, and it's a victory for Assad, it is not the end of the war. And the dangers that have come out of the Syrian war for Syrians and those in the region and all over the world continue.

MARTIN: Many people will have heard President Obama's press conference. The president was defending his position or his efforts to seek a diplomatic solution as opposed to using force. How do you think history's going to look back on the president's decisions here?

TABLER: I think history's going to look very poorly on the president's decisions. By any measure, Syria's a humanitarian disaster, the largest since the Second World War. But, you know, to people like in the hometown that I'm from in Pennsylvania, the two things that really are going to continue driving this home and showing that President Obama's policy was a failure is the combined threat of terrorism and that of migrants that are coming out of this fragmented and broken country.

And when these two streams crossed, they came to loosen up and to damage the societies throughout Europe that had been allies with the United States since the Second World War, brought Russia to the fore in the Middle East and even inspired, in the case of ISIS, a number of lone wolf attacks in the United States. And the war's not over. So I think that it's a stretch for President Obama to declare his Syria policy the best that we could have done.

MARTIN: What do you see as the next steps here, particularly given the incoming Trump administration's perceived closeness to the Russians?

TABLER: Right. I would imagine you're going to see two things. One is I would imagine a Trump administration will resurrect or implement what's called the Joint Implementation Group agreement, which was signed in late August and early September of this year but was not implemented when the U.S. accidentally bombed the regime position in the eastern part of Syria and then the Russians bombed an aid convoy coming into Aleppo. It's a quid pro quo. The U.S. agrees to target terrorist groups in Syria with Russia and synchronize their missions in exchange for aid deliveries to the opposition. They might have better luck doing that. So that's the first step.

The second step could be, and this would be more controversial, the cutting off of covert aid program to the Syrian rebels. President-elect Trump has been critical of that. That would deny the rebels at least some U.S. military equipment. But cutting off that program would also deny the U.S. vital intelligence on those groups that are throughout Syria and could lead to unintended consequences for our intelligence gathering.

MARTIN: That's Andrew Tabler. He's with the Washington Institute for Near East Policy. He's the author of "In The Lion's Den: An Eyewitness Account of Washington's Battle With Syria." Mr. Tabler, thanks so much for speaking with us.

TABLER: My pleasure. Transcript provided by NPR, Copyright NPR.