Rick Hanson, author of Buddha’s Brain and other books linking Buddhist teachings and scientific research, wrote a good introduction to the second noble truth of the Buddha, the causes of stress, discomfort, and suffering. You can find his article here: The Second Noble Truth-The Noble Truth of the Cause of Suffering
Thanissaro Bhikkhu, a well known translator and Buddhist teacher, has a detailed discussion of the causes of suffering in a chapter from his book on the Four Noble Truths. The first thing he points out is that the origin of distress and suffering is in our minds, not in the world. You can find that chapter here : The Second Noble Truth