Occupation is the seizure and control of another country by a powerful invading military. Might does not make it right.
The occupational disease required by the occupiers and their supporters can be treated by occupational therapy, which would be the study and application of morality.
There is a simplistic formula to determine rightness of action. One test is the result of an action, or "you shall know them by their fruits." The Ten Commandments are also a good standard. Occupiers feel good if they are not the one suffering from 4 million cluster bombs dropped in three days. It is a short life, and at its end, everyone may be challenged to account for his or her actions.