Tsar Nicholas I ordered Russian forces to occupy the Danubian Principalities of Moldavia and Wallachia (present-day Romania), in response to the Ottomans' refusal to allow a Russian protectorate of Turkish Christians.
Editors. "Ottomans declare war on Russia when they invade Moldova and Wallachia". The Literary Encyclopedia. First published 01 July 2011
[http://www.litencyc.com/php/stopics.php?rec=true&UID=4950, accessed 25 November 2015.]