What would have happened if either or both the Amu Darya and Syr Darya in Central Asia had supported an early Bronze age type (eg 3rd and 2nd millennium BC) civilization, similar to the ones that grew up around the Nile, Tigris/ Euphrates, Indus, and Huange He?
The "Bronze Age" refers to the period and style, so they don't actually have to use Bronze.
Why did this not happen?