An alien civilisation

I have found the aliens who have put the rubbish down the side of my sons bed.

They had created a civilisation in the radioactive wasteland that exists there.  I suspect that there were several there making use of the unique ecosystem(s) in the world underneath his bed, but due to the great ‘Underbed war’ only one species survived.  But in a lesson that the rest of our planet must learn, they too destroyed the environment they lived in.  And now they too are extinct, and all that remains are the ‘Underbed wastelands.’