On March 3, 1924, the city of Rijeka, the largest city on the northern Adriatic, was officially annexed to the Kingdom of Italy, marking a significant event in the post-World War I rearrangement of territorial boundaries. This annexation was part of the broader territorial losses suffered by the Kingdom of Serbs, Croats, and Slovenes (later known as the Kingdom of Yugoslavia), as it lost areas such as Istria, Zadar, and various islands to Italy as stipulated in the Rapallo Treaty. These changes reflected the nationalistic ambitions present in the region at the time, showcasing the ethnic tensions surrounding the ownership of these areas.

The Free State of Rijeka, established as a result of the same treaty, had a complex political history. It was recognized by all major world powers of the time and operated with its own flag, coat of arms, and currency, known as the Rijeka crown. This political entity spanned just over 20.8 square kilometers and housed around 52,000 residents, indicating a relatively small but politically significant area in the Adriatic region. Its establishment was seen as an attempt to address the contentious border disputes in Central Europe following the dissolution of empires during and after the Great War.

Rijeka's subsequent transfer to Italy, however, was not acknowledged in later treaties, such as the Rome Agreements between the NDH (Independent State of Croatia) and Italy in 1941, which meant that Rijeka remained Italian during World War II. This historical context emphasizes the ongoing territorial complexities in the Balkans and Northern Italy, revealing the region's turbulent history shaped by multiple national identities and evolving geopolitical landscapes.