The Russo-Ottoman War of 1710-1711 broke out as a result of the Great Northern War, which pitted the Swedish Empire of King Charles XII of Sweden against the Russian Empire of Tsar Peter I. Charles invaded Russian-ruled Ukraine in 1708, but suffered a decisive defeat at the Battle of Poltava in the summer of 1709. He and his retinue fled to the Ottoman fortress of Bender, in the Ottoman vassal principality of Moldavia. Ottoman Sultan Ahmed III declined incessant Russian demands for Charles's eviction, prompting Tsar Peter I of Russia to attack the Ottoman Empire, which in its turn declared war on Russia on 20 November 1710.