Russia interfered the internal affairs of Poland. During the Iran campaign they hindered the Crimean Army passing through the Caucus and occupied the Azak Castle, moreover Russia allied with Austria and Sultan Mahmud I decided to campaign against Russia on 16^th June 1736.

Banyaluka Victory was won on 4^th August 1737. The Russian forces attacked the Balkans and Crimea but they were defeated and retreated. Belgrade Castle was recaptured on 1^st September 1739. As the Ottoman Empire defeated the Russian Army on the Austrian front; Russia requested peace. The Ottoman Empire signed the Belgrade Treaty on 18^th September 1739 with Austria and Russia. According to the Belgrade Treaty; the Azak Castle would be left to Russians, the lands that Russia captured during the war would be given back to the Ottoman Empire and the Russians would not keep fleet of trade ships in the Black Sea. France supported this agreement and the privileges given to France were augmented.

The last years of Mahmud I passed in peace. But, the fires in Istanbul damaged the city. 800 houses in Bolat and Fener were burned in the great Istanbul fire on 28^th December 1745. In another fire, occurred five years later, some quarters and historic palaces of Istanbul were completely burnt (4^th February 1750). The great Istanbul earthquake occurred on 3^rd September 1754. During this earthquake, Istanbul was shaken for 14 times in 5-6 days. The cupolas of Ayasofya, Bayezid and Fatih Mosque were also damaged.