"The gods themselves fought the first war..."

See The Aryans and here. (Scroll down.)

"Thus did the gods war on each other..."
-"Star of the Sea," II, p. 557.

"'Dim memories of the conflict between cultures survived in myths of a war between the two divine races, which was finally settled by negotiations and intermarriage.'"
-11, pp. 565-566.

Poul Anderson presents first a version of the myth, then, secondly, a conversation between historians, who are also Time Patrol agents, about the origins of the myth.

First, the gods are real agents, then they are evolving ideas. Fiction looks at them both ways although not usually in a single narrative. "Star of the Sea" is the most comprehensive of the Time Patrol stories.