The main idea of Chariots of the Gods? can be seen from the subtitle that is shown on the cover of my copy. My copy has the subtitle “Was God an Astronaut?” As that implies, the main point of this book is that the gods of many ancient cultures were really alien space travelers. Von Daniken argues that space travelers visited the Earth in ancient times and that the ancient people took them to be gods. Throughout the book, he offers evidence that, in his view, supports this theory.
One argument that Von Daniken makes is that there are things, like the Egyptian pyramids and the stone heads on Easter Island that could not have been made using ancient technologies. On pp. 114-5 (in Chapter 8), he says that the island did not have the trees needed to make rollers or the number of people needed to do the work and that its natives could therefore not have created the moai. He claims that we can infer that alien space travelers landed there because
An orally transmitted legend tells us that flying men landed and lit fires in ancient times. The legend is confirmed by sculptures of flying creatures with big staring eyes.
Another argument in the book is that various ancient artworks actually shown alien space travelers. He argues that things that archaeologists say are fanciful representations of gods are actually pictures of what the ancient people really saw. As he asks on p. 31
why did the primitive peoples create figures in bulky suits with antennae on their heads independently of each other?
His answer to this rhetorical question is that they all saw similar aliens and drew pictures of them.
Finally, Von Daniken says that many of the things that are described in the Bible can best be understood when we think of aliens with advanced technology. For example, he thinks that the biblical story of Sodom and Gomorrah was an account of aliens destroying a population they did not like. As he says on p. 35,
Let us imagine for a moment that Sodom and Gomorrah were destroyed according to plan, i.e. deliberately, by a nuclear explosion.
He says this might have been done by the aliens
to destroy some dangerous fissionable material and at the same time to make sure of wiping out a human brood they found unpleasant.
Overall, what Von Daniken is saying in this book is that aliens visited the Earth in ancient times, accounting for many of the mysteries of the ancient world and forming the basis of the religious beliefs of many humans.