If the show had a bit more honesty about it, we would have had a scene where Lexa, wanting to teach her Nightbloods a little history, takes the children, and Clarke out for a ride.
They reach the bombed out remains of another city, one much larger than whatever Polis might have been. We can see the range of devastation. They can sit on a hill and look down upon it.
Lexa tells the children how it used to be a great city, full of people, how the land they live on was once part of a great nation that stretched from one ocean to another. But. The people who built that nation weren’t honest. They were greedy and arrogant. They’d stolen the land from others, the ones who came before them. She tells them how the people were subjugated, murdered, pushed out of their land, their way of life, their homes and left to all but die out.
When Aden asks ‘why,’ she explains, looking directly at Clarke, at how the invaders had superior weapons, how they thought the natives were savage and inferior. They thought nothing of taking what they had, destroying their way of life, because the invaders saw themselves as superior, of more value.
But even if the natives were savages, if you can even believe that word, they were not without value. They were not inferior. They deserved to live and to grow and to thrive. They weren’t monsters. And they did their best to protect one another and what they had made and were proud of.
‘But the invaders stole it all from them?’
‘Yes, they did.’
Clarke says nothing the entire journey.
The Doctor Is Out 