 The earliest evidence of warfare between two groups is recorded at the site of Nataruk in Turkana, Kenya, where human skeletons with major traumatic injuries to the head, neck, ribs, knees and hands, including an embedded obsidian bladelet on a skull, are evidence of inter-group conflict between groups of nomadic hunter-gatherers 10,000 years ago.Humans entered the Bronze Age as they learned to smelt copper into an alloy with tin to make weapons.In Asia where copper-tin ores are rare, this development was delayed until trading in bronze began in the third millennium BCE.