Developed five major gameplay features for the snakkze/1870-Hearts-of-Iron-IV-Mod repository, focusing on enhancing historical depth and regional balance in Hearts of Iron IV. Work included implementing a new South American Historical Alliance, refining Argentina’s initial military setup, expanding Brazil’s content with slavery-related mechanics, and enriching Paraguay’s traits and ideas. Leveraged data-driven configuration and localization pipelines using YAML and text-based scripting to ensure accurate faction alignment and narrative consistency. All updates were delivered without introducing bugs, demonstrating careful attention to stability and gameplay variety. The work improved localization coverage and starting-state balance, supporting increased player engagement and historical accuracy.