Thucydides was highly concerned with the relations among states. However the modern form of diplomatic history was codified in the 19th century by Leopold von Ranke, as the leading German historian of the 19th century. Ranke wrote largely on the history of Early Modern Europe, using the diplomatic archives of the European powers (particularly the Venetians) to construct a detailed understanding of the history of Europe wie es eigentlich gewesen ("as it actually happened."). Ranke saw diplomatic history as the most important kind of history to write because of his idea of the "Primacy of Foreign Affairs" (Primat der Aussenpolitik), arguing that the concerns of international relations drive the internal development of the state. Ranke's understanding of diplomatic history relied on the large number of official documents produced by modern western governments as sources, which he argued should be examined in an objective and neutral spirit.
In the early 20th centuries, work by prominent diplomatic historians such as Charles Webster, Harold Temperley, Alfred Pribram, R.H. Lord and B.E. Schmitt were mostly concerned with the events such as the Napoleonic Wars, the Congress of Vienna and the origins of the Franco-German War. A notable event in diplomatic history occurred in 1910 when the French government start to publish all of the archives relating to the war of 1870. The Bolsheviks in Russia published key secret papers from the Allies in 1918.
Ranke's understanding of the dominance of foreign policy, and hence an emphasis on diplomatic history, remained the dominant paradigm in historical writing through the first half of the twentieth century. This emphasis, combined with the effects of the War Guilt Clause in the Treaty of Versailles (1919) which ended the First World War, led to a huge amount of historical writing on the subject of the origins of the war of 1914, with the involved governments printing huge, carefully edited, collections of documents and numerous historians writing multi-volume histories of the origins of the war. In the interwar period, most diplomatic historians tended to blame all of the Great Powers of 1914 for the First World War, arguing that the war was in effect everybody's responsibility. In general, the early works in this vein fit fairly comfortably into Ranke's emphasis on Aussenpolitik.
Historian Muriel Chamberlain notes that after the First World War:
She adds that after 1945, the trend reversed, allowing political, intellectual and social history to displace diplomatic history.