Irrigation systems gave them water and controlled the floods of the rivers. without the irrigation systems the floods would have been detrimental to their societies. they collected water which they could use for farming and for the first time, there was a surplus of crops. the crops gave them food and also things to trade which helped their economy.
because they wanted to rule over the Americans and the Americns were already rebellling and they wanted to stop them.
National concerns shifted to overseas aggression
