From the Wikipedia:
"Axial Age (from the German Achsenzeit) is a term coined by the German philosopher Karl Jaspers. It refers to broad changes in religious and philosophical thought that occurred in a variety of locations from about the 8th to the 3rd century BC.
According to Jaspers, during this period, universalizing modes of thought appeared in Persia, India, China, the Levant, and the Greco-Roman world, in a striking parallel development, without any obvious admixture between these disparate cultures. Jaspers identified key thinkers from this age who had a profound influence on future philosophies and religions, and identified characteristics common to each area from which those thinkers emerged.
The historical validity of the Axial Age is disputed. Some criticisms of Jasper's include the lack of a demonstrable common denominator between the intellectual developments that are supposed to have developed in unison across ancient Greece, Israel, India, and China; lack of any radical discontinuity with "preaxial" and "postaxial" periods; and exclusion of pivotal figures that do not fit the definition (for example, Jesus, Muhammad, and Akhenaten). Despite these criticisms, the Axial Age continues to be an influential idea, with many scholars accepting that profound changes in religious and philosophical discourse did indeed take place but disagreeing as to the underlying reasons. To quote Robert Bellah and Hans Joas, "The notion that in significant parts of Eurasia the middle centuries of the first millennium BC mark a significant transition in human cultural history, and that this period can be referred to as the Axial Age, has become widely, but not universally, accepted."
1. From the Wikipedia:
"Jaspers presented his first outline of the Axial age by a series of examples:
Confucius and Lao-Tse were living in China, all the schools of Chinese philosophy came into being, including those of Mo Ti, Chuang Tse, Lieh Tzu and a host of others; India produced the Upanishads and Buddha and, like China, ran the whole gamut of philosophical possibilities down to materialism, scepticism and nihilism; in Iran, Zarathustra taught a challenging view of the world as a struggle between good and evil; in Palestine the prophets made their appearance from Elijah by way of Isaiah and Jeremiah to Deutero-Isaiah; Greece witnessed the appearance of Homer, of the philosophers—Parmenides, Heraclitus and Plato,—of the tragedians, of Thucydides and Archimedes. Everything implied by these names developed during these few centuries almost simultaneously in China, India and the West
Jaspers argued that the Axial Age gave birth to philosophy as a discipline.
Jaspers described the Axial Age as "an interregnum between two ages of great empire, a pause for liberty, a deep breath bringing the most lucid consciousness" It has also been suggested that the Axial Age was a historically liminal period, when old certainties had lost their validity and new ones were still not ready.
Jaspers had a particular interest in the similarities in circumstance and thought of its figures. Similarities included an engagement in the quest for human meaning and the rise of a new elite class of religious leaders and thinkers in China, India and the Mediterranean.
These spiritual foundations were laid by individual thinkers within a framework of a changing social environment. Jaspers argues that the characteristics appeared under similar political circumstances: China, India, the Middle East and the Occident each comprised multiple small states engaged in internal and external struggles. The three regions all gave birth to, and then institutionalized, a tradition of travelling scholars, who roamed from city to city to exchange ideas. After the Spring and Autumn period and the Warring States period, Taoism and Confucianism emerged in China. In other regions, the scholars were largely from extant religious traditions; in India, from Hinduism, Buddhism, and Jainism; in Persia, from Zoroastrianism; in the Levant, from Judaism; and in Greece, from Sophism and other classical philosophies.
Many of the cultures of the axial age were considered second-generation societies because they were built on the societies which preceded them."
2. A critical quote
"In my view the change from divine immanence (divinity within the world) into transcendence (divinity beyond the world) has provided this biggest transformation, it has split the spiritual from the material along hard lines, and made the spiritual inaccessible except under controlled gatekeepers. Since then the physical world has been stripped of any and all divinity, a desacralised carcass left to be scavenged by the vultures of communism and capitalism."
- Hwitgeard 
Origin of the idea of Axial Age
From the Wikipedia:
"Jaspers introduced the concept of an Axial Age in his book Vom Ursprung und Ziel der Geschichte (The Origin and Goal of History), published in 1949. The simultaneous appearance of thinkers and philosophers in different areas of the world had been remarked by numerous authors since the 18th century, notably by the French Indologist Abraham Hyacinthe Anquetil-Duperron. Jaspers explicitly cited some of these authors, including Victor von Strauß (1859) and Ernst von Lasaulx (1870). He was unaware of the first fully nuanced theory from 1873 by John Stuart Stuart-Glennie, forgotten by Jaspers' time, and which Stuart-Glennie termed "the moral revolution". Stuart-Glennie and Jaspers both claimed that the Axial Age should be viewed as an objective empirical fact of history, independently of religious considerations. Jaspers argued that during the Axial Age, "the spiritual foundations of humanity were laid simultaneously and independently in China, India, Persia, Judea, and Greece. And these are the foundations upon which humanity still subsists today."
Jaspers identified a number of key thinkers as having had a profound influence on future philosophies and religions, and identified characteristics common to each area from which those thinkers emerged. Jaspers held up this age as unique and one to which the rest of the history of human thought might be compared."
William Irwin Thompson:
"The Axial Age, with its global epiphany of prophets, from Orpheus and Pythagoras to Isaiah II, Buddha, Lao Tzu and Quetzalcoatl, seems to mark a critical turning point in the evolution of consciousness, for now the individual soul seems capable of knowing and expressing a higher truth than the received wisdom of the ancestors, the idols of the tribe.
Eric Havelock has described this transition as the evolution from the life-force of the Homeric thymos to the Socratic psyche:
At some time toward the end of the fifth century before Christ, it became possible for a few Greeks to talk about their ‘souls’ as though they had selves or personalities which were autonomous and not fragments of the atmosphere nor of a cosmic life force, but what we might call entities or real substances (Havelock, 1991, p. 197). Orphism was the vehicle in which this transition from thymos to psyche became articulated in hymns and instructions to the living on how to make their passage in the realm of the dead.
Orphism was a religion with a belief in immortality and in posthumous rewards and punishments. So far so good. But it had a more individual doctrine than that. Hades, with its prospect of torment and feasting, was not the end. There was the doctrine of the circle of birth, or cycle of births, and the possibility of ultimate escape from reincarnation to the state of perfected divinity (Guthrie, 1993, p. 164).
The figure of Orpheus, like that of Pythagoras or Quetzalcoatl, is a being of legend, so his story is more myth than history and serves as an allegorical performance of the truths to be passed from an initiate in the mysteries to the aspiring novice. Like Quetzalcoatl in Mesoamerica, he is a reformer who seeks to eliminate human sacrifice and carry humanity forward in its evolution from sorcery and blood magic to myth and a more stellar spirituality.
Just as Enkidu was warned not to partake of the food of the dead, less he be trapped in their underworld, so Orpheus is warned not to look back as he seeks to bring his beloved into light. In the esoteric practice of yoga nidra — the yoga of sleep meditation — the realm of imagery is an intermediate world of perception and deception, and only the realm of the nadam, of the cosmic sound, can enable the practioner of yoga to reappropriate the realm of deep dreamless sleep in the waking state of clear mind — a state of consciousness called samadhi.
Orpheus, as a musician of the heavenly harp given to him by Apollo, is an initiate of this cosmic sound — this music of the heavenly spheres — but according to the mysteries, our human star nature has been mixed with the ashes of the Titans at our emergence on Earth, and so humanity is a dyadic and contradictory creature. Our spirit is split between body and soul, between Orpheus and Euridyce. Because our star spirit has been captured in the vestiges of the elemental spirits of earth and matter, we must rescue it by shifting consciousness away from the concrete density of visual imagery to the higher realm of imageless music. But Orpheus looks back, seeking to hold his soul in sight, and so he loses her entirely. As he returns to earth, alone and embittered, he spurns the love of women and becomes a lover of men. The metaphoric complementarity of male and female as a trope for the polarity of the incarnate being is lost.
This mythic trope, as allegory for initiates, is describing a blocking of the union of ego and psyche, or waking mind and dreaming mind, in a psychological implosion of the ego in narcissism: same is bonding to same in a projected form of self love. But the male body, beautiful or not, can never serve as an answer to the problem of death. Just as the Goddess Ishtar sought her revenge against the male-bonding and defiance of the heroes Gilgamesh and Enkidu, so now the Maeneads seek their revenge against the violation of archaic women’s mysteries.
The blood sacrifice that the reformer Orpheus had sought to eliminate is inflicted on him as he is torn to pieces by the Maeneads — those vestiges of the neolithic.
In the terms of Jean’s Gebser’s schema for the evolution of consciousness,
Orpheus is the figure that marks the transition from the Magical to the Mythic structure of consciousness.4 But the collective wins out, and just as the Renaissance was followed by the Inquisition and a new baroque economy of slavery\ with its extravagant display of wealth, so Orpheus’s Apollonian reforms are followed by sacrificial rituals and his story is reappropriated into a cultural narrative of Dionysian ecstasy. The psyche remains trapped in the intermediate realm of imagery and the mind’s identification of consciousness with imagery — the familiar world in which ‘seeing is believing’.
But human spiritual evolution is not entirely stopped, and the reforms of the Axial Age are partially absorbed as Greek culture carries on with its transition from the Homeric thymos to the Orphic psyche — from the Bardic oral culture of the Archaic era to the new literate culture of the sacred text of the Classical era. As Steve Farmer has argued, it is the very portability of the new writing materials that serves to construct the Axial Age and spread the new values from India to Greece with Pythagoreanism in one direction, and from India to China with Buddhism in the other direction of the Silk Road.5 Indeed, in the evolution of consciousness from oral culture to literate civilization, the sacred text itself becomes the oxymoron that embodies our contradictory human nature. The text exists in the realm of imagery and is visually read, but it calls us back to a recollection (anamnesis) of our stellar nature. Death itself becomes less biological and collective — as it was in the neolithic and megalithic eras of collective burials — and becomes in the Classical era, more psychological and personal matristic culture of the sacrificial dying male and the enduring Great Mother."
The invention of freedom by Zoroaster
Alexander Bard has some great video lectures where he explains how Zoroaster was the first to stress human freedom, and free the believers from the tradition and constraints of ancestor worship. From here on, the son could be different from the father and 'innovate' (and much later, the daughter). Bard is a conservative futurist. This, from Imperium Press, is a vision from 'archaistic conservatives', who like some progressive tendencies like the primitivism of John Zerzan, seeks to identify the bifurcation that made humanity stray from the traditional path:
"In each culture, the transition from Old Age to New Age took the same basic form, but the paradigm is the transition from the Indo-Iranian cults to Zoroastrianism. The Indo-Iranian familial cults had changed but little from Coulanges’ archaic Aryans; they were orthopraxic, particularistic, centred on the hearth in the domus, and constitutive of the state cults. Conscience did not enter into the regulation of conduct—each House Father performed the rites as he had received them from his father. He was such a rigorous formalist, performing the rites with such exactitude, that certain formulae were sufficiently old that he no longer understood their meaning. This is what Max Weber called the magical religious paradigm,7 which does not traffic in ideas of “true” or “false”, but in ideas of “ordinary” and “uncanny”. Within this paradigm, conduct is essentially automatic and formulaic; one might compare this with Julian Jaynes’ “bicameral mind”.
Into this ur-traditionalist paradigm was introduced Ahura Mazda. Ahura Mazda was not the innovation of Zoroaster, but was re-framed by him as the synthesis and culmination of the two other “ahuras”, Mithra and Varuna.10 Ahura Mazda was now the greatest of the three lords, the lord of Wisdom. But Zoroaster went further. Not content simply to elevate one deity, he recast the whole pantheon, particularly the venerated “daevas” such as Indra, as demons and illusions,11 to where there could be but one omnibenevolent god, Ahura Mazda. And yet, there is evil in the world. Not content to simply call this the absence of good, Zoroaster hypostatized all the lesser malevolent spirits into one, Angra Mainyu, the apotheosis of evil, whose real name Ahriman must be written upside down.
The depth of this world-shattering transition must be underlined. We have here the invention of freedom—man must now make a choice between the force of absolute good and the forces of absolute evil.12 He is no longer bound by the religion of his fathers; he is free, absolutely free, to go his own way. But he can only go his own way, he can only make this choice, on the basis of conscience. Man’s conduct is no longer circumscribed by his relationship to others, by where he sits in the network of familial ties. He has been freed, and his moral compass is now within himself, and himself alone13—we have here the invention of the individual. The seed of the Reformation has been planted, and it is only the hardness of the Aryan soil in which it was sown that will delay its flowering — but flower it will. We have more. Religion is no longer primarily about propitiating a god (carrying out the rites, i.e. obeying commands), but before the rites, it is about a transcendent right and wrong (belief, “truth”, the narrativized “explanation”). We have here the invention of the proposition nation, identity as defined above all by belief, by the truth. And because the truth is the same for a fire-worshipping Parsi as it is for a tadpole, religion based on truth ceases to be a constitutive principle for a distinct people, but at least irrelevant to it, and at worst hostile to it. There is still more. The stakes of this choice, this infant sola fide, are ultimate, but the consequences of the choice follow primarily in the next life. Prayers are said and the god invoked not primarily for worldly goods, but for otherworldly goods, constraining the powerful and casting his eye away from this world—it is a magnificent piece of what Nietzsche will call “slave morality”. In the demotion of this world, we have here the abstraction of man from his immanent reality—no longer is he a mere dirt farmer, or a merchant, or even a king, but he is, in his essence, something not of this world.
The reader will have already seen where this is going. In the introduction of freedom, of the individual, of the proposition nation, and in the abstraction of man from his brute facticity, from his thrownness, we have seen the advent of liberalism."
From the Wikipedia  :
Armstrong, Karen (2006), The Great Transformation: The Beginning of our Religious Traditions (1st ed.), New York: Knopf, ISBN 0-676-97465-1. A semi-historic description of the events and milieu of the Axial Age.
Graeber, David (2011), Debt: The First 5000 Years, Brooklyn: Melville House Press.
Jaspers, Karl (1953), The Origin and Goal of History, Bullock, Michael (Tr.) (1st English ed.), London: Routledge & Keegan Paul, LCCN 53001441. Originally published as Jaspers, Karl (1949), Vom Ursprung und Ziel der Geschichte [The origin and goal of History] (in German) (1st ed.), München: Piper, LCCN 49057321.
Provan, Iain (2013), Convenient Myths: The Axial Age, Dark Green Religion, and the World That Never Was, Waco: Baylor University Press, ISBN 978-1602589964.
Eisenstadt, S. N. (Ed.). (1986). The Origins and Diversity of Axial Age Civilizations. SUNY Press. ISBN 978-0887060960
Hans Joas and Robert N. Bellah (Eds), (2012), The Axial Age and Its Consequences, Belknap Press, ISBN 978-0674066496
Halton, Eugene (2014), From the Axial Age to the Moral Revolution: John Stuart-Glennie, Karl Jaspers, and a New Understanding of the Idea, New York: Palgrave Macmillan. ISBN 978-1-349-49487-3
Muesse, Mark (2013), The Age of the Sages: The Axial Age in Asia and the Near East (1st ed.), Minneapolis: Fortress Press, ISBN 978-0-8006-9921-5.