Eternal War — Benjamin W. Schenk

The book is about family of immortals that have been around for 66 million years. They are fighting an endless war with their arch-enemies, the cavemen. The cavemen have been around even longer and they feel like they are the rightful rulers of Earth, since they were the first intelligent beings on the planet. They want to enslave mankind, and Bejine's immortal family is the only thing between them and their rule of the Earth! The immortals and the cavemen have been fighting their secret war for millions of years, out of sight of the modern humans. Their battle goes public, as the cavemen try to capture some of the daughters of Bejine, and they are joined by a small group of modern humans, that find out to their surprise that the immortals have not only lived forever but they are extremely hard to kill! Surprises await modern Earth in the 'Endless War'.