I may be splitting hairs, but "chronic fatigue" is a symptom. When its aetiology is unknown it is often classified as CFS. I would not be surprised to find that as medicine progresses many cases of CFS become re-classified.
Certainly, stress would exacerbate any symptoms of fatigue.
Yes, that's pretty much what I said. With the addition that if you look at the overall evidence it does seem to be pointing towards stress as the cause.
In the absence of an underlying vulnerability, it would seem pretty unlikely that stress alone would be sufficient to cause CFS. Many people have very stressful lives (including being refugees, being under regular fire, etc) without getting CFS.
The same can be said for PTSD. Whether or not chronic stress leads to hypocortisolism and burnout/CFS seems to be whether or not dealing with the stress is in the best interests of the organism (https://www.ncbi.nlm.nih.gov/pubmed/15950390), along with other factors such as time since onset, nature of the stress, personality factors, etc.
Stress-related disorders are quite common among the military and refugees (higher level of prevalence than the general population).
Certainly, stress would exacerbate any symptoms of fatigue.