The main drive for the Italian expansion in the Adriatic sea was irredentism. Basically, after the unification and the creation of the Italian Kingdom in 1861 (completed with the annexation of Rome in 1970) a lot of Italian speaking people were still living in Austro-Hungarian empire, in particular the city of Trieste and Trent but also a lot of Italian speaking minorities along the Dalmatian coast. Basically most of these territories were subjects of the former Venetian Republic and Italian people were mostly concentrated in the main urban areas, making the most of the local ruling elite and middle class, opposed to rural inland where Slavic language people were the majority. So between the end of the 19^th and the first decade of the 20^th century a lot of political movements and cultural associations grew up in Italy and Italian speaking minorities in the Austro-Hungarian Empire seeking to unify all the Italian populations under the Kingdom of Italy, financing school and education projects or celebrating Italian history and spreading the main themes of the Risorgimento and all sorts of anti Slavic and Austrian propaganda. The expansion in the Adriatic was seen as a natural progress of the wars of unification of the 19^th century, especially because the historical enemy was the same Austro-Hungarian Empire and because it was based on a cultural-linguistic concept of Italianity, so in the eyes of the nationalists and irredentists the Kingdom of Italy had the rights to fight for a complete unification of all the Italian populations under the same political entity. This was also the main reason why Italy started the WW1 in 1915 (one year after the declaration of war) and switching sides to go against the Austro-Hungarian Empire. At the end of the war, the Italian kingdom managed to gain the cities of Trieste and Trent but a huge mass movement inspired by war veterans and nationalists started calling the Italian victory a mutilated victory, because parts of the territories that were supposed to be given according to the [Treaty of London](https://en.wikipedia.org/wiki/Treaty_of_London_(1915)) were not accomplished. This movement was the core of what later became the Fascist party.

Another aspect that is important to keep in mind is the imperialistic policy. After the unification in the 1870's and especially during the 1880's the Italian governments realized they needed to compete with the rest of the European powers on the ground of foreign policy and military expansion, but Italy was still behind in terms of technological and industrial advancement compared to France, Germany and especially United Kingdom. The main logic in this era was that in order to grow and prosper economically a State had to pursue an imperialistic policy, because the concept of progress and wealth of a country was totally connected to its political and military power. This is one of the reasons behind the Italian colonial missions in east Africa and the wars against the Ottoman Empire which lead to the annexation of Libya in 1911. In the logic of the Italian nationalists at that time, the Italian Kingdom had to consider the Mediterranean sea as a legitimate field of expansion because of historical ties with the Roman empire and the Italian republics in the middle ages and Renaissance. These were the main lines of the nationalist propaganda at the time, and inspired many poets and writers as well as the public opinion into believing that it was totally normal for Italy to submit other populations around the Mediterranean sea either because there were local Italian minorities (and Italian speaking people lived almost everywhere in the Mediterranean) or because those lands were once part of Italian republics or the Roman Empire.

These aspects along with economical and demographic reasons (tenths of millions of Italians during this period emigrated to North and South America because of poverty) shaped the Italian foreign policy between 1870 and 1940. This doesn't mean that everyone in Italy was nationalist at that time (especially the socialist party and part of the Church establishment held different positions) , or that every Italian speaking person in the Austro-Hungarian Empire wanted to be an Italian citizen, but the core of the economic and military elites were inspired by this kind of mentality.