This is something I've been contemplating. Philosophy, as we know it, largely comes from the Greeks. Before them most of what might be considered philosophy is mixed with mythology and theology. This is not to say that philosophy is unique to Greece, but they did do more on the subject than many others.
I've been wondering why that is, what is special about Ancient Greece that led to this development, philosophy qua philosophy without immediate recourse to theology or mythology.
I would say that there were *parts* of Greek philosophy that were without immediate recourse to theology or mythology. But frankly, it is what is called "Sophist" philosophy - really, pre-Socratic Greek thought - which was most removed from theology/mythology. Plato's philosophy, to my reading, is very, very religious. There is a reason why Catholic theologians were quick to adopt Platonism. And then, too, many pre-Socratic traditions were very, very mystical, e.g. the Pythagorean cult.
As to what was special about Ancient Greece, typically, the story you hear is that the nature of Greek city-states gave rise to a class of public teachers because there were many young men who required an education on how to be a "virtuous man" so that they could lead lives of public service. Since Athens was famously the birthplace of democracy, and had many young men who were getting ready to enter public, political, life, there was a substantial demand for such teachers, and it was in Athens that we see a flourishing, although clearly this cannot be the whole story. But even in the arts we see a movement away from mythology - the rise of Athenian tragedy as an example, with its emphasis on humanistic themes.
And as you say, this sort of philosophy was in no-way unique to the Greeks. The Chinese and Vedic traditions have many examples of this sort of thing. I have only a cursory knowledge of non-Western traditions, but my impression is that the Chinese, more than the Greeks or Vedic traditions, produced the most work that was totally removed from theology or mythology. Indeed, Confucianism is one of the oldest schools of thought that continues to be extremely influential, and at the same time, is largely secular. Sure, Confucianism is couched in ultimately spiritual terms, but mostly it concerns itself with practical, secular considerations. The Vedic traditions were a mixed bag in this regard, but there were strong forms of non-theological, non-mythological thought. To my limited knowledge, you would see this most clearly in Advaita Vedanta. Indeed, there were pockets of outright atheism and naturalism in Advaita Vedanta.
