The Morgan Line was the line of demarcation set up after World War II in the region known as Julian March which prior to the war belonged to the Kingdom of Italy. The Morgan Line was the border between two military administrations in the region: the Yugoslav on the east, and that of the Allied Military Government on the west. After 15 September 1947, the Allied Military Government was composed of both the British Element Trieste Forces (BETFOR) troops from the United Kingdom and the Trieste United States Troops (TRUST) from the United States.

The Julian March, also called Julian Venetia, is an area of southern Central Europe which is currently divided among Croatia, Italy, and Slovenia. The term was coined in 1863 by the Italian linguist Graziadio Isaia Ascoli, a native of the area, to demonstrate that the Austrian Littoral, Veneto, Friuli, and Trentino shared a common Italian linguistic identity. Ascoli emphasized the Augustan partition of Roman Italy at the beginning of the Empire, when Venetia et Histria was Regio X.