What is the main problem?

I think that the main conflict has to do with class struggle. The tension between different social classes and societal expectations pervades the novel. Before Papa's death, Esperanza makes a clear distinction between hers and Miguel's social status using the metaphor of them standing on either side of a river which they can never cross. During that time in Mexico, social class was a hierarchy of wealth and skin tone, but in the United States, everyone in Esperanza's camp is poor. The only distinctions are between the Mexicans, the Japanese, and workers from other parts of the United States, like Oklahoma. Esperanza struggles to adapt to the lower social class because she initially refuses to share her possessions and argues with Miguel. While most of the Mexican immigrants in Esperanza's camp have come the United States go for a better life, Esperanza's social status is lower in California than it was in her native Mexico. Nonetheless, Esperanza eventually comes to accept her position as she matures.