Wold Newton Research has established that Barsoom is actually situated in an alternate universe very "close" to that of the WNU, one that contains Amtor and Thanadar as well as Mongo and which for some reason allows relatively easy travel between the two (emphasis on relatively).
The planet Barsoom itself is in many ways a "fallen" world, one that still shows signs of an ancient and incredibely sophisticated civilization that (among other things) dug the canals that supply water from the poles to the arid plains as well as building vast machines that maintain the dying planet's atmosphere. Several humanoid (more or less) races call Barsoom home and at least some of them can have viable offspring with homo sapiens from Earth.
Scholars hold that Barsoom is also the location of many stories traditionally associated with Mars, including the invaders at the heart of The War of the Worlds by H.G. Wells and the adventurer Gulliver Jones (see below).
- Wikipedia article on Barsoom
- The Tarzan/John Carter/Pellucidar/Caspak/Moon/Carson of Moon Chronology by Win Scott Eckert
- H.G.Wells' Barsoom (article in the ERBzine about Barsoom) by Den Valdron
- Apocryphal Barsooms (Its All The Same Mars!) by Den Valdron
- Gulliver Jones on Barsoom? by Den Valdron
- A Cartographic Study of Barsoom
- Post Modern Barsoom
- Wikipedia article on Mars: The Home Front a crossover story between H.G.Wells and Barsoom.