Okay, so, this is a pretty simple alternate history post: how could Romania become an empire (colonial or otherwise), and how could this empire last until at least the early-mid 20th century?
-Dracula gets more support and wards off Ottomans more effectively
-Minhea, son of Vlad, secures power in Wallachia and marries into control of Moldovia. He consolidates power and his son capitalizes on the Battle of Chaldiran in 1514 to hand Ottomans a major defeat in 1516, pushing into Bulgaria
-Marriage of Minhea's grandson into Hungarian royal family with Transylvania as dowry and land-based follow-up to Battle of Lepanto pushes Draculean/Romanian forces into Varna, Sofia, and towards Belgrade. Ruthless treatment of Ottoman opponents and survivors under Vlad IV is the stuff of legends, including a recreation of Basil II's 'Bulgaroctonos' event. By the death of Vlad IV, although Adrinople and Greece remain Turkish, much of modern Bulgaria and parts of Serbia are in Romanian hands. A dream of a Romanian port on the Mediterranean come into being at Thessaloniki.
-Matthias I begins the 'Golden Century' following the failed Siege of Vienna by Sulieman the Magnificent. Romanian forces use the siege to begin threatening Istanbul itself, taking Thessaloniki, Mount Athos, Adrinople, and trapping the Sultan's army in Europe. Persian forces take advantage of the situation as Sulieman passes away and two of his sons take control - one in Europe, one in Asia. While the Romanians make like ghosts and attack almost exclusively at night, the Ottomans in Europe suffer withering casualties. Less than a third of their army returns to Istanbul intact and a civil war begins between Selim and (an imposter posing as a living) Bayezid. The war allows the Romanians to consolidate the whole of the Balkans south of Pecs and Szeged and east of Timiosara, also including Chernivtsi and Odessa along with much of SW (OTL) Ukraine.
Why don't go for the final prize in itself, so the City of the Men's Desire? Constantinople will be the key for Romania to become definitely an Empire in effective swing.