1. Dodecanese Islands: In 1911, Italy seized control of the Dodecanese Islands, a group of islands in the Aegean Sea that were previously under Ottoman rule.
2. Libya: Italy had already established suzerainty over Libya in 1911 and, through the Treaty of Ouchy in 1912, secured full sovereignty over Libya.
3. Eritrea and Somalia: These two territories were already Italian colonies before Mussolini's rise to power.
4. Ethiopia: In 1935, Italy invaded Ethiopia, resulting in the Second Italo-Ethiopian War. By 1936, Italy had conquered and occupied Ethiopia, incorporating it as a colony into the Italian Empire.
5. Albania: In April 1939, Italy invaded and annexed the Kingdom of Albania, establishing a protectorate government under Italian control.
These were some of the major territorial acquisitions made by Mussolini during his time as the leader of Italy.