it was gulf of mexico before there was a usa

 The Gulf of Mexico has been named since the 16th century, when Spanish explorers began to map the region following the arrival of Hernán Cortes in 1519. The term arises because this vast expanse of water was located east of the lands we know today as Mexico, which were then dominated by the Mexican Empire.

Since when is it called the "Gulf of Mexico"?

XVI Century: The name "Gulf of Mexico" appears on maps and historical documents since the first Spanish explorations. European cartographers began to use it to designate this semi-finished basin, because of its proximity to the Mexican territory.

Although there was no Mexico as a country (independent since 1821), the name referred to the Mesoamerican region under Spanish control and linked to the Mexican empire.

It was named before the existence of the United States

The name "Gulf of Mexico" was established long before the formation of the United States in 1776.

During the sixteenth and seventeenth centuries, the area that today includes the states of Texas, Louisiana, Alabama and Florida was part of Spanish and French colonial territories, and had no relation with the future country.

This reinforces that the Gulf of Mexico, both as a geographical region and nomenclature, has historical roots that precede the creation of the United States.

Conclusion

The Gulf of Mexico has carried its name for more than 500 years, long before the United States existed as a nation. This term reflects its historical and geographical connection with Mesoamerican lands, being a denomination that persists since the first maps elaborated by European colonizers.