The so called 'Avante Garde' 'Out' or 'Free' jazz really grew from a deliberate attempt to move to a more African based aesthetic and away from mastery of Euro based values prevalent in the earlier, 'Common Practice' phase usually broken into 'the Swing era, various forms of 'Bop' and also called 'Mainstream'.
There were a tremendous variety of approaches to Iconoclastic Jazz, often rooted in a particular community of origin. Thus there was one approach among native born New Yorkers, another from Midwesterners such as the AACM in Chicago or the BAG from St. Louis and then there was another from L.A.
As circumstances eventually drove artists from all these far flung communities to New York, a gateway to work overseas, some blending occurred.
To my mind, a most significant element of this profoundly diverse period was a commonly held belief that method should be subordinate to purposeful expression and , in the most compelling instances, the expression intends to be a deep union with the mysteries of the natural world and a capacity for allegory through sound.
This is often the meta intent of the most compelling work and the great wealth of technique extension on nearly every facet of sound craft is almost a happy bonus to the real core value of the work.
And that sense of reverence for the natural world, that readiness to embrace the mysteries and that readiness to live a disciplined uncompromised life despite the added weight of challenge it puts on shoulders will always, to my mind mark the idiom at its very best.