Which major civilization developed in the region indicated on this map during the classical era?

The Olmec

Explanation:

The Olmec culture was the civilization that developed during the Preclassic and Classic period of Mesoamerica. Although vestiges of its presence have been found in large areas of Mesoamerica, it is considered that the Olmec nuclear area - metropolitan area - covers the southeastern part of the state of Veracruz and west of Tabasco, on the coasts of the Gulf of Mexico

1200 a. C., and the most recent ones are approximately of the year 400 a. C. The Olmec civilization was constituted mainly around 3 ceremonial centers: San Lorenzo, La Venta and Tres Zapotes, besides manifesting in other places as Laguna de los Cerros.

i think it would be a

uncle sam would be tossing and turning in his grave : *)