Why were there food shortages in the united states during world war 1

In the introduction of becoming mexican american, sanchez draws from stuart hall's notion of cultural identity (pg. 12-13). hall asserts that identities are enmeshed in "becoming and of being." they are subjected to the elements and context of history. explain what you think he means by the idea of becoming and being and explain how context fits into comprehending the american concept of manifest destiny.