Much of what is distinctive about modern evil is - ultimately - the work of demons: I mean the global conspiracy (the 'Illuminati') and their mass of minions and henchmen that constitute the secular New Left which dominates the West.
These are the strategists of evil - taking a long view - their plan being to subvert and damage The Good en route to their plan to invert Good and evil and achieve the self-chosen damnation of mankind...
(...The ugliness of Modern Art being asserted as beautiful, the beauties of traditional art mocked as patriarchal or Kitsch - truth being labelled as hate speech - politically correct lies as a deeper kind of 'truth'; chastity, marriage, family being denigrated as oppression - and the ever expanding, subsidised and officially endorsed license, transgression and manipulations of the sexual revolution as admirable and courageous liberations.)
But not all modern evil is demonic: some is merely monstrous.
As usual Tolkien can help clarify things. In Lord of the Rings, demonic, strategic evil is represented by Sauron and his enslaved Ringwraiths, and hollowed-out and possessed servants such as The Mouth of Sauron (and behind Sauron, excluded from The World itself - the actual Satan of Morgoth).
But evil monsters are also encountered - and these are 'tactically evil' in the sense of utterly selfish and seeking of their own immediate gratification. Old Man Willow is a monster of selfish greed, resentment of hobbits, and desire to dominate and presumably eat them. The Barrow Wight is some kind of wicked ghost, hoarding treasure and striving to perform human sacrifices. The Watcher in the Water seems to be a malign predator merely.
The worst of monsters is, of course, Shelob - the giant spider (descendent of Ungoliant) whose evil is an insatiable hunger for the life and energies of everything else that exists; without foresight or goal - to eat until there is nothing else left alive - when she would die of starvation...
The link between demons and monsters is that the demons will use the monsters for strategic ends; rather as the demonic Illuminati (of politics, royalty, Vatican, media, law enforcement etc) used the monster Jimmy Savile - but the pattern is replicated in many places and at many levels.