During Austro-Hungarian occupation of Serbia in World War I, Stanojević escaped to Sankt Petersburg, where he taught at the university as a visiting professor.

[1] After the war, in 1919, Stanojević resumed his chair as professor of National History at the University of Belgrade until 1937, the time of his death.

His basic orientation was the medieval history of Serbia and the Serbian lands, primarily the early Middle Ages and the time of the Nemanjić dynasty.

He authored six hundred and sixteen works, and the most popular are Byzantium and the Serbs and The History of the Serbian People.

Stanojević wrote many books about history of Serbia and history of the Serbs, including: He also organized and arranged the "Great National Encyclopedia of Serbs, Croats and Slovenes" ("Velika Narodna enciklopedija Srba, Hrvata i Slovenaca"), which was the first work of the kind written in Serbian language.