The Central Plain was a massive battlefield for the vassal states of Eastern Zhou (770-221 BC). By coercing and absorbing each other, these states experienced an era characterized by warfare, military reforms and consolidation. The craft techniques of the powerful bronze weapons reached its zenith during the Eastern Zhou. Many vassal states developed complex logistical systems and innovated in the art of warfare, supported by efficient government bureaucracies. These institutions were newly-established to supply and control large military forces.