September is the month many latino countries declared their independence. For example, the countries of Central America, declared their independence the 15th of September of 1821. As to why we celebrate Hispanic Heritage Month the United States it is because it celebrates the long and important presence Hispanic and latino Americans have in the U.S. Although this is only the tip of the iceberg as to why we celebrate Hispanic Heritage Month, I hope this helps you understand as to why, and I also encourage you to research a little more of the topic.