In June 1945, the Anglo-American Allies and the Jugoslav Government agreed upon establishing a bi-zonal occupational regime in the Julian March. One of the main points of the agreement was the so-called Morgan line, the provisional boundary which was to divide the British/American and the Yugoslav zones. During the first two years of occupation, the relations between the two neighbours remained rather tense, with many incidents (some of which serious) occurring along the line. Even after the ratification of the Italian Peace Treaty, in September 1947, the situation did not improve significantly. The military détente along the border of the Free Territory of Trieste came only after the Tito-Stalin split and the subsequent, gradual rapprochement between Yugoslavia and the West. Using original archival sources (mainly British), this essay provides the reader with an extensive overview on the frontier incidents which took place in the Julian March and the Free Territory of Trieste from mid-1945 until 1949 (when the last clashes involving Allied troops occurred).