Theme is usually not my first priority in a game and Explorers & Exploiters is probably my least thematic game. One would think that a civilization game would be able to pick and choose suitable themes from the history of man. However, I didn't find any for the game flow of Explorers & Exploiters, where settlers build cities that are razed by barbarians and rebuilt again.
Instead, the inspiration mainly came from Sid Meier's computer game Civilization, where a city's expansion is dependent on the resources linked to it and where barbarians appear to destroy improvements and attack cities.
This was also apparent in the Sprue Challenge judge review of the game, where the lack of theme may have prevented Explorers & Exploiters from reaching beyond the semi-finals. Perhaps a retheme should be considered?