The city's decline in population after World War I was mainly due to economic difficulties caused by the withdrawal of Austro-Hungarian military and bureaucratic facilities and the dismissal of workers from the shipyard.

Under the Italian Fascist government of Benito Mussolini, non-Italians, especially Slavic residents, faced a political and cultural repression, and some fled the city of Pola and Istria altogether.

After the collapse of Fascist Italy in September 1943, the city and the province were occupied by the German Army as part of the Operational Zone of the Adriatic Littoral.

In the 1930s, the province of Pola enjoyed an economic revival based on minerary exploitation (coal in Valdarsa) and infrastructure investments.

The Via Flavia – from Trieste to Pola – was enlarged and reduced in distance; the railways were improved and the water facilities increased with the new "Acquedotto Istriano".