U.S. President Donald Trump's decision to pull out from Syria is probably the beginning of a whole new period in the Middle East. The decision put the international coalition against Daesh in a very difficult position, along with the People's Protection Units (YPG), Iran, Israel and Saudi Arabia. Some of those have supported the U.S., some others opposed to it, but their common point was that the presence of American troops in Syria somehow justified their presence in Syria, too.
All these actors have had a hard time justifying why they want to remain in Syria, even after the American pullout. Besides, the retreat increased the risk of seeing Turkey, an American ally, engage in a comprehensive operation against the YPG, which is supported by the U.S. Similarly, the risk of seeing Turkey, with which Russia has become a strategic partner in Syria, and the regime forces, which are Russia's allies, confront one another is bigger now. Moreover, the Europeans who think they can benefit from the U.S.' departure and Saudi Arabia are now trying to be more active in the area. In fact, they all have to admit that Russia is almost the only player whose position will determine the future of the Syrian crisis.
When Trump noticed that his decision amplified the risks of interstate wars, he decided to slow the process down. This allowed a negotiation process for the future of the zones near the Turkish border and areas now controlled by the YPG. These negotiations have two main players: the U.S. and Russia. In fact, those who have suffered the most from the current situation in those areas are Turkey and the Syrian people. Those two are only looking for security and stability for a foreseeable future, while the two major powers are looking to find a way to preserve what they have in the Syrian theater.
Involved players have divergent expectations, but they have to agree on a common road map. The most difficult part of the talks is how to secure the border zones in a way that will satisfy Ankara. One may find different methods to secure such an area, like having a demilitarized zone or a buffer zone, among others. No matter what, what counts is to make sure that terrorist organizations will no longer be present in those territories, so they will not start calling these territories "cantons" or "provinces" again, in the hope of creating a Basque-like or Scottish-like fait accompli. It is probably obvious for everybody now that Turkey will never allow that to happen.
It seems that the U.S. and Russia will finally agree on having a powerful central government in Syria. This government will have to remain equal vis-a-vis Saudi Arabia and Iran, the Kurds and Arabs, the Alawites and Sunnis, and so on. If such a model can indeed be crafted and if Bashar Assad proves capable of running this model, he will be able to remain in power for a while. If not, he will be replaced. In a sense, no matter who rules in Damascus, Syria as a whole will be designed as a big buffer zone in the middle of the region.
Syria will be divided into influence zones, such as they did in Ukraine. We know that in the latter, some provinces are now controlled by Russia and the rest by Westerners, mainly Germans and Americans. A similar future is to be expected in Syria. Of course, as in Iraq, the U.S. remains more influential than anyone else. In Syria, Russians will have the last word. Israel will be allowed to secure its borders, while Saudis and Iranians will be asked to leave. In this configuration, Turkey may play the role of the holder of balance.
The presence of troops on the ground is obviously helping the negotiating parties at the table; but at the end of the day, problems are resolved during negotiations, not battles. Maybe that's why Trump's surprise decision will open a period in which bargaining and not the use of weapons will be at the center of Middle Eastern politics.