Thus , the Kingdom of Romania began with the reign of King Carol I of Romania . Thus , the Kingdom of Romania began with the reign of King Carol I of Romania who gained Romanian 's independence in the Romanian War of Independence , and ended with the abdication of King Michael I of Romania in 30 December 1947 , imposed by the Soviet Union with the tacit and secret , implicit consent of its allies ( as a result of the Yalta Conference and secret agreements ) . As such , it is quite distinct from the Romanian Old Kingdom , which refers strictly to the reign of King Carol I of Romania , between 13 March 1881 and 10 October 1914 .