Russian Empire had obtained recognition from the Ottoman Empire of the Tsar's role as special guardian of the Orthodox Christians in Moldavia and Wallachia. Russia now used the Sultan's failure to resolve the issue of the protection of the Christian sites in the Holy Land as a pretext for Russian occupation of those Danubian provinces.

Shortly after he had learned of the failure of Menshikov's diplomacy toward the end of June 1853, the Tsar sent armies under the commands of Field Marshal Ivan Paskevich and General Mikhail Gorchakov across the River Pruth into the Ottoman-controlled Danubian Principalities of Moldavia and Wallachia. The United Kingdom, hoping to maintain the Ottoman Empire as a bulwark against the expansion of Russian power in Asia, sent a fleet to the Dardanelles, where it joined a fleet sent by France. On 16 October 1853, having obtained promises of support from France and Britain, the Ottomans declared war on Russia.

The Danube campaign opened brought the Russian forces to the north bank of the River Danube. In response, the Ottoman Empire also moved its forces up to the river, establishing strongholds at Vidin in the west and Silistra in the east, near the mouth of the Danube. The Ottoman move up the River Danube was also of concern to the Austrians, who moved forces into Transylvania in response. However, the Austrians had begun to fear the Russians more than the Ottomans. Indeed, like the British, the Austrians were now coming to see that an intact Ottoman Empire was necessary as a bulwark against the Russians. After the Ottoman ultimatum in September 1853, forces under Ottoman General Omar Pasha crossed the Danube at Vidin and captured Calafat in October 1853. Simultaneously, in the east, the Ottomans crossed the Danube at Silistra and attacked the Russians at Oltenița.