Unseen Warfare refers to the traditional Christian perception of good and evil forces - angels and demons - struggling over the salvation of the soul.
(Unseen Warfare is also one of the titles of a book on this subject which - in my version - is attributed in terms of having been written by Lorenzo Scupoli, edited by Nicodemus of the Holy Mountain, and revised by Theophan the Recluse - then translated from the Russian by E Kadloubovsky and G.E.H. Palmer.)
Naturally, Unseen Warfare is absent from the discourse of secular modernity - since this has no belief in the soul, therefore nothing over which unseen forces might be at war.
But who does believe in Unseen Warfare? Here are a few examples:
1. The Bible.
2. Pretty much all the mainstream Christian Churches, until the past few decades.
3. The Saints and Holy Fathers.
4. C.S Lewis, JRR Tolkien and Charles Williams.
5. Fr. Seraphim Rose.
One important aspect of Unseen Warfare is that it is, or may be, unseen.
In other words, it may be going-on (is going on), and good or evil may be victorious - yet this may not be perceptible to other people.
One consequence is that (according to the traditional wisdom encapsulated in the discourse regarding Unseen Warfare) evil needs primarily to be conceptualized in terms of aims and effects on the destiny of the soul, and not in terms of effects on the psychological and physical states of 'other people'.
And an an evil man, a damned soul (like Lawrence Wentworth in Charles Williams' Descent into Hell) does not necessarily do more harm to others than the average person, and does not necessarily make 'other people' less happy or more miserable.
And what is an evil entity?
The secular modern conception of evil is that evil involves being excpetionally nasty to other people - it is the opposite of altruism.
The modern idea of evil is someone like Hitler who did a lot of harm to a lot of people.
However, modernity can explain being nasty to other people only in terms of selfishly pursuing one's own gratification at the expense of others - which is something we all do, to a greater or lesser extent. Therefore evil - even Hitler - is seen as relative and quantitative: the evil are those who are the least altruistic and the most selfish.
The traditional concept of extreme purposive evil is not about harming the happiness of others in this world, but a situation more like that of a damned soul dedicated to achieving the damnation of other souls. That is, roughly, a demon.
This objective stands in the starkest possible contrast to that of a good (angelic?) entity - who is a saved soul that aims at the salvation of other souls.
Therefore, from the traditional perspective of Unseen Warfare the difference between good and evil entities and aims is not relative and quantitative but, on the contrary, absolute and qualitative.
And the primary battle ground, the main site of moral struggle, is the human mind - and not human society.