His research activities range from fundamental work on papal diplomatics of the Middle Ages to the history of the country up to the Second World War.
In 1958, under the supervision of Peter Acht, he was awarded a doctorate in philosophy in Munich with the thesis Contributions to papal chancery and documents in the 13th century.
[3] One year after his doctorate, Herde's first scientific essay Gestaltung und Krisis christlich-jüdischen Verhältnisses in Regensburg am Ende des Mittelalters was published.
In Rome he established friendly relations with Hermann Goldbrunner, Dieter Girgensohn, Norbert Kamp, Arnold Esch, Rudolf Hiestand and Rupert Hacker.
His farewell lecture, in which he took a critical look at recent developments in German higher education, was held on 16 June 2001 at a symposium in the Museumszentrum Lorsch [de].
[7] With the edition and investigation of the formula books of the Audientia litterarum contradictarum he published a two-volume and almost 1400-page Munich habilitation thesis.
[15] Together with his student Thomas Frenz, he published in 2000 the letter and memorial book of the Passau Cathedral dean Albert von Behaim of 1246.
[20] Herde investigated the background of the failed appeals of Franz Schnabel to Heidelberg and Hermann Heimpel to Munich.
[24] According to their research, Bosl had behaved in a highly system-compliant manner under National Socialism and falsely presented himself as a resistance fighter.
[25] Dirk Walter criticised the lack of comparison of Bosl's career during the Nazi era with that of other colleagues like Theodor Schieder.
[26] Herde presented numerous works on the history of the Second World War, including two monographs on the secret flight connection between the Axis Powers and Japan ('The Flight to Japan', 2000) and on Japanese occupation policy in Southeast Asia during the Second World War and its consequences ('Greater East Asian Prosperity Sphere', 2002).
[28] Herde noted in his study that "despite all controls and despite censorship [...] Japanese rule [...] in the Philippines was not totalitarianism of a Soviet or Nazi nature".
[29] For a decade, Herde researched the months of August and September in the National Archives and Records Administration in Washington, where millions of pages of listening material are stored.
This resulted in a study published in 2018 on the triangular relationship between the European Axis powers, Japan and the USSR during the Second World War.
The sources it contains are telegrams sent between the Foreign Ministry in Tokyo and its diplomatic or consular missions abroad, intercepted and decoded by US agencies from 1942 onwards.