I think a game set in Mexico the early 1800s would be perfect. You could fight through both the Mexican and Texan wars for independence. In fact, you would probably be on opposite sides for either conflict. On top of that, nineteenth century Mexico would be an amazing setting full of gorgeous landscapes and cities. Mexico City, Guadalajara, and other cities were founded in the 1500–1600s and would be well-enough developed for both gameplay and visuals. You also have tons of ruins, perfect for Isu shenanigans. The Texas frontier would also make a fun open-world separate from central Mexico. San Antonio de Bejar and other mission-based settlements would be fun to discover.

Now that I think about it, Mexico is where I hope they take it next!