[4] Delbrück vigorously opposed the policy of the Prussian government in dealing with the Danes and the Poles, with the result that he was twice subjected to disciplinary penalties as a professor and a civil servant in Prussia.

At an early stage of the First World War, he became pessimistic regarding the possibility of victory, except by a military and political strategy and tactics of a purely defensive character.

His works were not translated into English for some time, hence his reputation among professional military theorists in English-speaking countries is not held in the same esteem or significance as Clausewitz.

Singular conclusions on ancient warfare challenged historiography in so far as he tried to show that the figures for armies in antiquity were inflated in the original sources, and that, contrary to what is stated in most writings, the winner in a battle usually had more troops than the loser.

Consequently, he gave completely different interpretations to some of the most famous battles in history, like Marathon, Gaugamela, and Zama by concluding that Rome's vaunted advantage over "barbarians" rested, not so much in their discipline and refined tactics, but rather in their superior logistical support.

He applied the analytical tool to the wars of Frederick the Great and concluded that their numerical inferiority made the Prussians pursue a strategy of exhaustion.

He was very critical of his country's strategic thinking, and he averred it would have been preferable to seek victory in the East, gain minor objectives in the West and then sue for peace.

In a clearer reference to the historical figure, in Mel Brooks's comedy The Producers, Hans Delbrück is the name of the man to whom Franz Liebkind sends a letter by carrier pigeon.

In Victor Serge’s novel Unforgiving Years (Les Années sans pardon) the character Herr Schiff—an old German professor loyal to the Nazi regime, demoralized and disoriented in war-ravaged Berlin in the closing days of the Second World War—rereads Hans Delbrück’s The History of Warfare: "Lately, it was true, the sense of most of what he read escaped him; but being incapable of inattention, the mechanical act of reading acted upon him like a sedative.