John Carter of Mars destroyed all of that
terraformation equipment that worked on
principles of the ether and the eighth
ray to begin with.

No one quite figured out how he got to
Mars to begin with, however the Martians
didn't have a chance once he got there.

By the time the Earth humans got there at
the turn of the 20th to the 21st in an only
slightly modified ATL from our own, there
were virtually no Martians left to kill
off with the chicken pox, leaving only a
few phantom-like telepathic chameleons as
a backdrop to the Earth humans.

Don't ask me how these Earth human colonists
then earlier or later became the Martians of 
the ultra-distant past.