Tarzan the Untamed: Book 7

Tarzan the Untamed was one of Burroughs' most controversial novels. The controversy stemmed from his blanket portrayal of Germans as stereotypical, unredeemable villains, one that was also extended to his contemporary science fiction novel The Land That Time Forgot. This portrayal, while perhaps understandable in wartime, ultimately ruined the market for his writing in Germany, where the character of Tarzan had formerly been quite popular. Burroughs' later introduction of heroic Germans into his subsequent novels Tarzan and the Lost Empire, Tarzan at the Earth's Core and Back to the Stone Age did little to repair the damage to his reputation there.

Previous novels in the series had dealt primarily with the ape-man's own affairs, while Tarzan the Untamed and later ones (beginning with Tarzan, Lord of the Jungle) would cast him as a protector and enabler of others.

Tarzan the Untamed introduced the lost civilization of Xuja, foreshadowing a pattern in later Tarzan novels. Of the six books before Tarzan the Untamed, two featured the lost city of Opar, but otherwise the series centered on Tarzan's adventures in his natural environment, the jungle. After Tarzan the Untamed, lost civilizations in remote parts of Africa became common in the novels. Such places tended to consist of two warring cities or kingdoms. (wikipedia.org)