Senkou no Night Raid

Shows that have spies/secret agents or focus on espionage. This list will be updated if there are other animes related to this.

*Spinoffs, sequels, and extra DVD bonuses are not included

Tales from the early Showa period (first 20 years of the reign of emperor Hirohito, who ascended to the throne 1926).
During this time, Japan encounters the world economic crisis, impoverishment, exploitation, political strife, rise of militarism, political opression, imperial expansion, and World War II.
Maybe one of the most interesting periods of Japanese history.
Only including titles that cover at least glimpses of the prewar period.

Suggestions for additional titles are welcome.

Anime that are based within the Taisho time period. Majority are historical with a couple involving magic/ and or fantasy elements.

The Taisho era marks further Western influences in Japan from clothing to democracy. Still, the country makes a push in China, taking both island territories and areas into the North. There aren't a lot of anime set in the relatively short Taisho-era, but military motifs are almost always present.