Stuff is happening in Syria again.
When the Syrian Civil War wound down a few years ago, the Assad regime was in control of the whole country except for three areas: The Kurdish-held areas in the eastern part of the country, a small Turkish occupied area in the north of the country, and the province of Idlib, which is held by rebels, most of whom are aligned with al-Qaeda. (The pro-democracy rebels are no longer a major force.) These areas are all governed by ceasefires which are violated constantly. Last year, Turkey invaded and occupied part of the Kurdish area. The rest of the Kurdish area is subject to a security agreement between Assad and the Kurds.
Over the last few years, Assad has slowly chipped away at the rebel territory in Idlib, and over the last few weeks, the rebel defenses have apparently fallen apart. (I've been busy with other things and haven't been monitoring the situation as closely as I did during the war.) About half of Idlib province has fallen to the regime, including the important cities of Maarat al-Nouman and Saraqib.
Assad has now captured the entire M5 road, which is the most important transportation line in the entire country, connecting the capital city of Damascus to the country's second largest city, Aleppo. Maarat al-Nouman and Saraqib both lie along the M5. Idlib province contains two other major roads: the M4, which connects Saraqib to the rebel-held city of Jisr-al-Shughur, and a road whose name I don't know, which connects Saraqib to Idlib City and then continues on to Turkey. Assad is currently trying to cut the Saraqib-Idlib-Turkey road, which would cut off Idlib City's supply lines and make it easier for him to besiege and eventually capture the city.
Turkey is understandably upset by this, since they don't like Assad and like having chunks of Syria that are occupied by Turkish and Turkish-aligned forces. It wouldn't surprise me if Erdogan's long term goal for Idlib province was annexation. He can't do that if Assad retakes it. The Turkish army is currently hightailing it to the Saraqib-Idlib-Turkey road so they can defend it from Assad.
I doubt that this will result in full-scale war between Turkey and Assad. (It definitely won't result in war between the US and Russia, so please nip the "oh god it's WWIII" comments in the bud.) Assad would certainly prefer to take Idlib City now if he can get away with it, but it's not in his interest to aggravate Turkey. He can easily take land from the rebels at some later date, but it will be much harder to take land that's directly occupied by the Turks. That being said, we live in a crazy world, so all kinds of things could happen.
I replaced the original news article with a map to make it easier to understand what's going on. Here's the article:
https://news.yahoo.com/erdogan-says-turkey-push-back-083542519.html