Dan II first took the throne in 1420, losing it in 1421, but regaining it that same year. He was primarily able to regain the throne many times because he was an able military commander in the field. In 1423, Dan II led an army against the invading Ottoman Turks, defeating them in battle. The Ottomans were invading in an effort to place Radu II back on the throne. In 1425, he again defeated the Ottomans, winning an important victory in a battle that was the first recorded mention of Wallachia using mercenaries in their army. In that battle, Dan II had employed a large number of Bulgarian soldiers. In the spring of 1427, Dan II removes Radu II from the throne for the last time, again defeating the Ottomans in battle, taking back the fortress at Giurgiu. In all likelihood, Dan II killed Radu II either during or after that battle, as the latter disappears from historical records afterwards. However, written accounts of the time are sparse at best, and it is not known for certain. On 3 June 1428, Dan II led an army against the Ottomans at Golubac Fortress, which ended with a treaty that would allow Dan II a semi-peaceful rule until 1432.