An indirect sequel to Edgar Rice Burroughs' John Carter series is his Venus series. A rocket launched from Earth towards Mars but pulled off course by lunar gravity falls towards the Sun, thus crossing the orbit of Venus which, fortunately, is close enough to land on. Before leaving Earth, Carson Napier had contacted Edgar Rice Burroughs because of the latter's known interest in Mars which presumably means his publication of Carter's manuscripts.
Despite this, Napier seems to be uncertain what he will find on Mars. However, the two series are definitely connected through other Burroughs works. Gridley contacts both Mars/Barsoom and the Earth's Core/Pellucidar by radio. He, Tarzan and others visit Pellucidar through the North Polar opening and ERB mentions this visit in the first Venus book.
Thus, half a dozen ERB series are concurrent and sometimes interactive, like a comic book universe.