This is all part of a larger conflict that will need resolving for lasting peace to be achieved
There are many ethnic, religious, economic and civil rights issues that have made the Syrian civil war so long lasting and complicated. But, when you consider the number of ISIS insurgents, the war is arguably an overspill from the Iraq War and part of the Saudi and Iranian proxy conflicts, sometimes call the Middle East Cold War. These issues will need to be addressed and dealt with, as will the problem of extremist groups that operate in this area that have further exaggerated the suffering and further complicated this conflict.
However, when you consider the presence of both the United States and Russia, backing opposing sides of this conflict, comparisons have been draw between the Syrian Civil War and Cold War era Germany. The opposing involvement of these same two aggressors in multiple proxy wars internationally, including the above mentioned Saudi and Iranian proxy conflicts, is a similar diplomatic landscape to the Cold War.
As the US moves to withdraw from Syria the country should recognise the apparent similarities to historical conflicts and attempt to not engage Russia in further proxy conflicts. Likewise the US should admit to their failings in Syria in regard to operations to further destabilise the country, such as Timber Sycamore, and attempt to not repeat those mistakes in further complex diplomatic situations, for example in Venezuela. Finally, the US should take further care not to be involved in confrontations that destabilise regions seeking diplomatic solutions over military ones.