Dia de la Raza, which translates to Ibero-American Columbus Day, is celebrated on Oct. 12 in Mexico with parades, dancing, parties and food. Dia de la Raza is also celebrated in the United States, but it is known as Columbus Day.
Dia de la Raza commemorates Christopher Columbus landing on an island in the Bahamas on Oct. 12, 1492, which he thought was India when he landed. Though Columbus died still believing that he had made it to India, he was the first to facilitate contact between Europeans and the inhabitants of the American continent.
Other countries celebrate Dia de la Raza as well, but the name varies by country. For example in Spain it is known as Hispanic Day, and in Argentina, it is known as Día de la Diversidad Cultural Americana, which translates to American Cultural Diversity Day. In Chile it is called Día del Descubrimiento de Dos Mundos, which translates to Day of Discovery of Two Worlds, and in Costa Rica, it is Día de las Culturas or Day of Cultures.
The overarching reason to celebrate on Dia de la Raza is the uniting of two worlds that took place as a result of Columbus' landing in 1492.