When The Martian Chronicles begins, everyone is in the right place—the humans are on Earth (in Ohio, in "Rocket Summer") and the Martians are on Mars (in "Ylla"). But things are about to change: people are building rockets, and by "The Summer Night," more and more humans are coming to Mars.
We see other examples of humans and Martians not getting along (such as earlier, in "Ylla" and later in "The Off Season"), but this is where most of the conflict happens. It's not a war, just some misunderstanding in "The Earth Men" and a little ambush in "The Third Expedition."
"—And the Moon Be Still As Bright" sets up some of the major questions that this story cycle addresses: is it right for humans to settle a place that's, you know, already inhabited? What's the right way to treat a different civilization? Is it possible to leave behind Earth conflicts? Turns out, finding a whole new-to-you world is pretty complicated.
This section runs from "The Settlers" to "The Luggage Store." Humans come to settle Mars and they bring with them all their stuff from Earth—trees, religion, new names for places, censorship, murder, and sadness for lost loved ones. Meanwhile, tensions are rising on Earth.
In the stories from "The Off Season" to "The Long Years," we see that Mars still hasn't quite become home for the settlers. So when war breaks out on Earth, just about everyone goes back. Sure, some people accidentally stay, like in "The Silent Towns" and "The Long Years," but those chapters just help emphasize how un-homelike Mars has become.
"There Will Come Soft Rains" shows us what happened to all the Martian settlers who went back to Earth: they've been turned into shadows on the wall. Wonder if they're regretting their decision now?
Here's the thing about Earth Men: they're survivors. In "The Million-Year Picnic," a few people have escaped from war on Earth and come back to settle Mars. Maybe this time Mars will really become home. Or maybe this colonization attempt is also doomed to failure. We have to admit, our fingers are crossed.