Final answer:
During the World War I (option B) era, G.K. Chesterton wrote pamphlets to counter German (option B) aggression. The British were concerned about Germany's expanding ambitions which threatened European stability and led to heightened militarization and eventual conflict.
Step-by-step explanation:
G.K. Chesterton and Historical Context
During the World War I era, G.K. Chesterton was asked to write pamphlets in support of England's efforts to stave off German aggression. This time was marked by a high tension in Europe due to Germany's territorial ambitions, threatening the balance of power established after the Napoleonic Wars. As Germany sought to expand its colonial holdings, these ambitions conflicted with those of other imperialistic powers, particularly Great Britain, and this friction eventually led to military buildups and the specter of war.
The correct answer to the fill-in-the-blank question is: During the World Wars, G.K. Chesterton was asked to write pamphlets in support of England's efforts to stave off German aggression. The term World Wars in the answer specifically refers to the First World War, as this was the period when Chesterton was active and when Britain was threatened by German military actions.