Answer
Ferdinand became King of Romania in 1914, following the death of his uncle, King Carol I. A member of the Hohenzollern-Sigmaringen dynasty, Ferdinand had served as the heir presumptive since 1889. His reign marked a period of significant change for Romania, including the country's entry into World War I in 1916 and its subsequent unification with Transylvania and other regions formerly part of the Austro-Hungarian Empire.