Who is in the wrong?

The demon king’s armies were pushing the Human Empire completely back.
The hegemony of this world was soon to be changing, or so it should’ve been.
But the humans performed the usual “last measure” ritual, and a hero has been summoned.
Ever since their summoning, the hero’s growth was exponential, and after years of fighting the battle has been balanced, and entered a stalemate.
But overall, the demons were superior, thus the stalemate won’t last long.
Especially when the Demon King is recognized as both the best expert of the lands as well as the best strategist.
So the Hero made up a powerful team, composed of the strongest elites of the human race, and started their journey towards the Demon King’s castle, in order to kill them.
Without the Demon King, the demon kin would be an easy target for the Humans, especially with help from other worlds as well.
So, the Hero’s party started to make their way towards the Demon King’s castle, by-passing the demon kin patrols, and armies.
But when the Hero arrived at the castle with the team, what awaited them was a horrible, and quick defeat.
The Demon King barely needed to release her aura and the humans fell one after the other, except for the Hero, who could still remain conscious.
Above their teammates unconscious body, the Hero glared with unimaginable anger at the Demon King.
“You monster!
Why are you hell-bent in causing so many deaths?! What’s the point of all of this!?”
The Hero shouted.
The Demon King just smiled.
“In order to stop the suffering of my people.”
She said.
“Suffering? What do you know about suffering?!
The many villages your people ravaged, burnt!
Your evil knows no bounds!”
The Hero, with teary eyes shouted.
“What do I know about suffering?
I grew up on this planet, back when it was ours.
Elves, dwarves, dragonians, and many more we all lived in relative peace, trading with each other, slowly advancing, opening up the skies.
Then, you all came here from the greater universe, with your flying ships that now are used defensively because just a branch of the clan remained here.
Then “war” erupted.
War a bit too much said, as you completely obliterated us, we barely managed to retreat to our Ancestral Mountain…
I trained for tens of thousands of years, to have a chance of regaining our homeland…and I will get it back..
Ask your Emperor, who are the true natives?
Also, demons…heh, for us you are all the demons.”
She said, slowly approaching the Hero.
As she stepped closer, chains appeared, locking up all the companions of the Hero, until only the Hero remained free.
“Y-y-y-you! Liar! That’s not true!
I’ve seen the atrocities you all have committed!”
The Hero shouted.
“It’s a war, what did you expect?
I know you aren’t from this planet, nor this universe, and seeing how your teammates are all females human or not, you must come from a very…rudimentary realm.
You take in whatever you like and ignore or disdain what you don’t like…
I’ve forbidden my troops the slaughter of civilians, women and kids alike, but…I am not there, bad things happen.”
The Demon King shrugged.
“You monster…
I won’t believe you, you must be lying because you want me to betray my people!”
The Hero said with disgust.
At this, the Demon King laughed.
“Oh, young kid, how naïve of you…
Want you to betray your people? I can handle you with my pinkie…
Also, “your people”? You aren’t from here, the moment I die, is when you “Sacrificed yourself to kill the great danger”.
How laughable…Hero…
It seems I need to train my generals better…”
She laughed, as she waved her hands, and chains bound the Hero completely.
With her strength, the Demon Kind quickly covered the battlefield, and thus the battle turned in the favor of the demons…
Soon, they will have reclaimed their lands…
Or so they proclaim.
Who is in the wrong?
Was it truly the humans who seem omnipresent in the universe the usurpers? The invaders?
Or were the myriad races, labeled as “demons” by the humans, the ones who try to conquer the lands?