In the Middle East , a variety of factors â '' including population growth , soil degradation , drought , cast bronze weapon and iron production technologies â '' could have combined to push the relative price of weaponry ( compared to arable land ) to a level unsustainable for traditional warrior aristocracies . In the specific context of the Middle East , a variety of factors â '' including population growth , soil degradation , drought , cast bronze weapon and iron production technologies â '' could have combined to push the relative price of weaponry ( compared to arable land ) to a level unsustainable for traditional warrior aristocracies .