During his reign, Sultan Ahmed II devoted most of his attention to the wars against the Habsburgs and related foreign policy, governmental and economic issues. Of these, the most important were the tax reforms and the introduction of the lifelong tax farm system (malikane) (see tax farming). Following the recovery of Belgrade under his predecessor, Suleiman II, the military frontier reached a rough stalemate on the Danube, with the Habsburgs no longer able to advance south of it, and the Ottomans attempting, ultimately unsuccessfully, to regain the initiative north of it.