Edgar Rice Burroughs was an American author, best known for his creation of the jungle hero Tarzan and the heroic John Carter, although he produced works in many genres.
Hundreds of years after the Kalkars came down from the moon to conquer Earth and set up a Communist-like dictatorship, mankind has been driven back to a pre-technology nomadic existence. The Kalkars have been pushed west across North America and now occupy a small strip of land along that coast.
The Red Hawk is the leader of the largest tribe of "Yanks," who worship the Flag and vow that the Kalkars will always be their enemies. They include decendents of humans who aided the Kalkars in this vow. This humans--descended from the villain of the first novel in the Moon trilogy--are called the Or-Tis.
When Red Hawk leads an attack on the Kalkars, the Yanks win a massive battle. But Red Hawk is captured. Escaping will involve allying himself with an Or-Tis. Later, Red Hawk falls for a woman who is also an Or-Tis. For both military success and personal joy, Red Hawk has to learn to set aside centuries of prejudice.
It's a fun novel--one that is impossible to read without thinking of the Star Trek episode "The Omega Glory." The massive battle between Yanks and Kalkars is one of Burroughs' best action sequence (in a career that's full of superb actions sequences). Red Hawk's climactic duel with a 9-foot-tall Kalkar is also fantastic.