The Gods of Mars by Edgar Rice Burroughs

If I was a bigger Burroughs fan, rather than merely a voracious reader over these many decades, I'd know which pulp magazine he serialized the John Carter tales for, probably Amazing Stories. If I cared enough, I could look it up. After reading enough of this story, you begin to detect the cliff hanger points where it probably was broken off until the next month.

Burroughs receives a mysterious message from his uncle, John Carter, and meets him at a hotel to get the latest account of life on Mars (ironically, I'm writing this a couple of days after the Curiosity landed on Mars). Carter is finally successful in achieving the proper spiritual or mental state which allows him to travel to Barsoom, and he hopes to be reunited with the beautiful Dejah Thoris once more.

Unfortunately for him, but perhaps good for Barsoom, he is transported to the area where travelers on their final pilgrimage to the Valley Dor, where they will meet their gods. He discovers his old friend, the green warrior Tars Tarkus there, and together they battle their way through the great white apes and carnivorous plant men to reach the lair of the Holy Therns, who take charge of (enslave) those of the lesser races that survive the journey.

So John Carter and Tars Tarkus battle the white men of Mars, then they finally escape from that place and JC ends up captured by the black race, who prey on the therns and the other "lower" life forms. After escaping from there, hoping to be reunited with his love again, he has to battle ambition and treachery in the City of Helium.

As Emily Latella used to say, "it's just one thing after another."