Problem: The development of irrigation and the adoption of iron tools during early Zhou Dynasty O caused increased conflict between local tribes over agricultural resources. O created a surplus of food in the region and allowed the population to grow. O caused rulers to wage more aggressive wars for control over iron and irrigation channels. allowed individual peasant families to farm successfully without the aid of the state. O meant that iron tools were used to trade for more lucrative goods on the Silk Road and irrigation facilitated better transport.