Final answer:
The nations that lost territory to form Yugoslavia were Italy, Austria-Hungary, Bulgaria, and the Ottoman Empire.
Step-by-step explanation:
The four countries that had land taken away to create the new nation of Yugoslavia after World War I are Italy, Austria-Hungary, Bulgaria, and the Ottoman Empire. Yugoslavia was created as part of the post-war restructuring of Europe and was intended to unify various Slavic groups such as the Serbs, Croats, Bosnians, Montenegrins, and others into a single state. Despite the intention of creating a unified nation of Slavic people, Yugoslavia's diverse ethnic composition and national tensions eventually led to its dissolution in the 1990s.