Why does this hispanic heritage month start on september 15? why do we have the celebration in the united states?

It's an anniversary of independence day for five Latin American countries, like Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua. As well as Mexico declaring its independence on September 16 and Chile on September 18. Kind of specific on the September months actually, More than 35 million people in us are Hispanic so maybe that's why it's so currently popular.