The working title of Fade To Grey was originally Final Contact 2, until I found a better one. It’s almost a sequel to that story, set a short time after it, and looking at another way alien species might screw up their planet so humans end up colonizing the whole galaxy.

In the The Future universe, Luddites destroyed Earth many centuries ago, and here, the Luddites among the aliens went even further, leaving the planet intact, but destroying all life on it, so it might as well have been destroyed too.

Ultimately, I just liked the image of the mechs spreading destruction around the planet, then heading out again like alien Johnny Appleseeds, spreading the seeds that would return life to a dead world.