The key date for the global bronze Age is 2400 BC. This is when the Great pyramid appears to have been built using access to high quality copper from Lake Superior. This was sufficient to underwrite a global metal working sea connected civilization we know as the Atlantean.
Yet the size and scope screams for the existence of a long prehistory that did not much depend on a metal trade and its natural currency the metal ingot. This prehistory was land based village agriculture without the threat of mobile cavalry..
That expansion took several thousands of years and took advantage of woodland soils. This includes Western China and all the Middle East and the Sahara. The loss of tree cover slowly eroded the hydraulic cycle and the presence of domesticated browsers prevented recovery. The end result was abandonment and movement into lands were irrigation was possible.
Because we are looking, we are picking up evidence of this huge earlier population and their tools.
This also readfily explains why First atlantean Chinese pyramid building is so far west. That was were the agriculture was.