A country we have come perilously close to not invading at all. We have done so, though. As early as the fourth century, Magnus Maximus, who was later to enter Welsh legend as Macsen Wledig, led an army from Britain into mainland Europe to seize the imperial throne. He specifically recruited more Brits for an attempted invasion of Italy and some of his forces ended up in action in what is now Slovenia, losing to the forces of Theodosius. And we did just scrape across the border from Italy at the end of the Second World War. In a confused situation in which Tito’s victorious Yugoslav partisans were taking back Yugoslav territory previously annexed by Italy, and even pushing on into territory that forms part of present-day Italy, passions were running high and the tensions that were to lead to the Cold War were already evident on the ground.
In this chaos, the disputed territory known as the Julian March was divided in two in June 1945 by the Morgan Line. Most of the area came under Yugoslav administration, but a thin western strip, including, for example, the present-day Slovenian town of Sezana, came under joint British-American control.
In 1947, at the Paris Peace Conference, the areas of Slovenia held by Britain and America were handed to Tito.