As I read "d'Aulaires Book of Greek Myths" to Véra, I am reminded of Paul Rosenberg's "Production vs Plunder", and how it interprets the history of religion and state; and it becomes painfully obvious to me, which was never mentioned when I was a kid, that the stories of Gods violently defeating other Gods by allying with other Gods — were the oral tradition remnants of stories of inter-ethnic strife, whereby one ethno-cultural group violently imposes it supremacy through wars and alliances, only to be eventually toppled by another group.
Greek mythology, like other less-documented polytheistic mythologies, is often retrospectively presented as some kind of structured view of the world, some sort of single coherent static religion where every God has a well defined role in the Universe. But nothing could be further from the Truth. Complex structures like established religions do not arise out of the divagations of some mad poet inventing random gods in drunken stupor. No, established religions they are the fruit of cultural, economical and political confrontations among and between many people rivaling for dominance, whether peacefully or violently. And this confrontation does not follow an orderly plan, but is a mess, a market, a war, an enterprise, and much more; a dynamic reality where gods are memes backed by money as well as swords, by farmers as well as intellectuals, by the inertia of large ethnic groups as well as the catastrophic action of charismatic leaders.
In the Greek Theogony, first comes Gaïa, a primitive cult to Mother Earth, not an active cult, but a memory of the very first religion of the first agriculturists. Then, her son, lover and husband Ouranos takes over; he is a Sky-God, a rain God — one old variant of so many conquering or domineering sky gods in so many mythologies. That again is the memory of a first conquest of the agriculturists by invading herdsmen and their Sky-Gods; you can tell who did the violent conquest by who ends up on top despite not being there first. Though in the very first conquest, the conquered were so probably so incompetent at fighting that they just surrendered without too much blood; balance of power is the fruit of long interactions.
There are other gods, the Titans, and some many-headed or one-eyed monsters, but they are "sons" to Ouranos and Gaïa, and Ouranos cast them into Tartarus. Historically, this sounds like this religion managed to eliminate two or more different families of religions, and violently repress or destroy their cults, maybe genociding or enslaving their followers. The many-headed monsters and the cyclops could have been animists, or people once led by a one-eyed leader or two, or a tribe of herdsmen known for their one-eyed sheep. The details are long lost. But once you understand myths as history compressed to stable memes by centuries of oral transmission by the victors (and to a lesser degree by other survivors), they are no longer arbitrary just so stories, they are the last witnesses of wars and invasions, alliances and natural catastrophes, from a time before history was written (at least by those who transmitted those myths).
That story when Kronos defeats his father Ouranos? One religion that was formerly repressed or subsdiary took over the dominant status from the previous Sky God. Kronos was the youngest of the Titans — a recent religion from a new set of migrants. He castrates his father Ouranos and throws his testicles to the sea (a detail omitted from d'Aulaire's expurgated retelling). There might have been an actual event where some King or High-Priest embodying the power of Ouranos was thus overpowered and castrated by another embodying the power of Kronos; or there have been a mass castration of enemies; or just killing of males; or just the descendants of the vanquished king (his notional seed) fleeing by sea; or some combination of the above, or something else. Oral history doesn't well distinguish between Gods and their cults, between the people and their leaders, between successive generations of leaders, between people with the same name, between prominent mountains and rivers of one people who tell a story, and prominent mountains and rivers of other people who appropriate and retell the story, or who tell it after having migrated.
Then, Kronos eats his children — maybe his priests try to claim for him the attributes of other gods, declare them but facets of that one god, and build a syncretic monotheism out of the many religions around; but that doesn't hold, and eventually he is toppled by Zeus, his "son in hiding", i.e. a newer secondary Sky God, worshipped in clandestinity — or maybe the very same Sky God as Ouranos, and also the same as Thor or Indra, just reimported from latter waves of migrants, distant cousins of the former, invading a few centuries later. Zeus, allied with his "siblings" once eaten by Kronos, i.e. with reestablished cults previously repressed, wins over Kronos; then most of the Titans refuse his reign, but Zeus and his allies prevails after a long war. Zeus even allies with some of the older gods (of animism?), but in the end casts them back to Tartarus, to "guard" the Titans; this episode might possibly correspond to the allies fomenting a rebellion by some people enslaved by their enemies, only to enslave most of them again after the victory. Indeed, animism survives in Greek Mythology, with nymphs and river Gods, spirits of trees and houses, though it remains secondary to institutionalized religion. Whatever happened, you have to imagine a long, messy ethno-religious strife, as the previous political supremacy is destroyed and the former vassals fight over who will or won't be dominant in the new order. Kronos may have been the Cretan power. Or not. I don't know. I don't know that anyone knows. It has stopped mattering that much many millenia ago. What still matters though is that we should understand human nature, and how culture is the condensate of the often violent confrontation of many influences.
However, Theogony is not all wars. A story goes that Aphrodite came from the sea; she does not acknowledge being the daughter of any other god yet she sits in the Pantheon equal to the greatest of them. — That story does not suggest a war; likely, the people who brought their love goddess Aphrodite came with some superior sea-faring technology and were adopted in the greater Greek commonwealth. Who were the seafaring people of the day? The Phoenician. And indeed Wikipedia says that Aphrodite is of Phoenician origin. So this interpretation of myths does lead to verifiable predictions. Some stories suggest Aphrodite was produced by the seed of Ouranos thrown to the sea — which seems to confirm the interpretation of the fall of Ouranos as a sea migration after the downfall of a mighty kingdom. Other stories claim that Aphrodite was a daughter of Zeus after all; this filiation is symbolic subordination; it probably was retroactively invented later, after the Phoenicians had been taken down a notch in the pecking order of the CommonWealth: indeed, Gods did take sides in the Trojan war (i.e. the most prominent leaders of each cult), and Aphrodite was on the defeated side of the Phoenician-related Trojans. Other peaceful gods include Dyonisos and Prometheus. Dyonisos brings wine and tells everyone how to make it. The much older god Prometheus once brought fire stolen from the thunder god Zeus (i.e. from a fire started by a thunderstorm), and taught men how to keep it. Sometimes, a wave of migrants joins a common culture through peaceful trade, by bringing some superior technology or another, and contributes with it a god or goddess to the Pantheon of the day — or become deified in recognition of their achievement.
Our successors in the far future, whether made of flesh or of digital patterns, will not study our detailed history. Their understanding of us will be based on gross summarizations, optimized for extracting and transmitting whatever meaning remains relevant to them, not for completeness or accuracy — in other words, on myths. Even if all the written and filmed documents of today survive, the picture they draw is far from complete, and far from accurate, and wouldn't be either necessary or sufficient to understand whatever there is to understand about our times. It too is myths, myths that we feed each other in order to manipulate each other in various ways. Consider how most of what has been written on the recent US election was partisan propaganda of some kind; and that is not at all specific to those US elections, just more blatant and obvious for the close, high-stakes contest. Understanding how to not to fall for the remnants of propaganda of the past is a good exercise to avoid falling for the overwhelming propaganda of the present.
PS (2017-09-07): Of course, historical clashes do not alone explain myths. The worldview, the beliefs, the values, the worries, the aspirations, of the tellers and retellers, that they wish to propagate onto others or that they blindly follow, are also part of these stories... and that's the whole point: there is no single force at stake in building and propagating myths. Describing the myths that reached us as flowing from a single coherent source, rather than emerging as a mish-mash of memes that evolved and fought each other, is itself an absurdity that flows from the superstitious judeo-christian notion of a "revealed truth".