Because the content of my book overlaps significantly with the experience of those suffering from Moral Injury, I have collected some excepts below that help explain the topic.

Excepts from Huffington Post article Moral Injury: The Crucial Missing Piece in Understanding Soldier Suicides
Rita Nakashima Brock, Ph. D. | Jul 23, 2012 11:06 AM EDT

Moral injury is not PTSD. The latter is a dysfunction of brain areas that suppress fear and integrate feeling with coherent memory; symptoms include flashbacks, nightmares, dissociative episodes and hyper-vigilance. PTSD is an immediate injury of trauma.
Moral injury has a slow burn quality that often takes time to sink in. To be morally injured requires a healthy brain that can experience empathy, create a coherent memory narrative, understand moral reasoning and evaluate behavior. Moral injury is a negative self-judgment based on having transgressed core moral beliefs and values or on feeling betrayed by authorities. It is reflected in the destruction of a moral identity and loss of meaning. Its symptoms include shame, survivor guilt, depression, despair, addiction, distrust, anger, a need to make amends and the loss of a desire to live.
Moral injury is not a clinical condition that can be medicated or cured by psychology. It requires the reconstruction of a moral identity and meaning system with the support of a caring, nonjudgmental community.

Excerpt from The meaning of moral injury.
One of the first research projects involving moral injury is reported in an article in the Clinical Psychology Review entitled Moral injury and moral repair in veterans. The authors define moral injury as β€œan act of transgression that creates dissonance and conflict because it violates assumptions and beliefs about right and wrong and personal goodness.” (p. 698)

Because of the moral dissonance that is experienced, the conflict gives rise to feelings of guilt, shame, and fear of being ostracized. An individual with moral injury may come to feel immoral, irredeemable, and un-reparable, or struggle with the belief that he lives in an immoral world.
The authors of this cutting edge research describe the circumstances that can give rise to moral injury as, β€œ[p]erpetrating, failing to prevent, bearing witness to, or learning about acts that transgress deeply held moral beliefs and expectations. This may entail participating in or witnessing inhumane or cruel actions, failing to prevent the immoral acts of others, as well as engaging in subtle acts or experiencing reactions that, upon reflection, transgress a moral code. We also consider bearing witness to the aftermath of violence and human carnage to be potentially morally injurious.” (p. 700)