The Russian-Turkish war of 1736-1739 was the result of the Russian effort to gain Azov and Crimea as a first step towards dominating the Black Sea. In several successful raids led by Marshal Munich, the Russians broke the resistance of the Tatars, cross the Dniester into Moldavia and in 1739 marched as far as the Moldavian capital of Jassy, which they captured. Austria entered the war in 1737 on the Russian side to get its share, but was forced to make peace with Ottomans at the separate Treaty of Belgrade, surrendering Northern Serbia and Lesser Wallachia, and allowing the Turks to resist the Russian push toward Istanbul. In return, the Sultan acknowledged the Austrian Emperor as the official representative for all Ottoman Christian subjects, a position also claimed by Russia. The Austrian pullout forced Russia to accept peace at Nissa, giving up Crimea and Moldavia, being allowed to build a port at Azov but not to build fortifications there or have any fleet in the Black Sea.
The Treaty of Belgrade was the peace treaty signed on September 18, 1739 in Belgrade, Serbia by the Ottoman Empire on one side and Austria on the other.
With the Treaty of Belgrade, Austria ceded Northern Serbia with Belgrade and Lesser Wallachia, gained by the Treaty of Passarowitz in 1718 to Turkey and set the demarcation line to the rivers Sava and Danube.
The Austrian withdrawal forced Russia also to accept peace with Treaty of Nissa, by which Russia gave up the Crimea and Moldavia, but was still allowed to build a port at Azov, again gaining a foothold on the Black Sea.