Ferdinand I of Romania, nicknamed "The Unifier", became King of Romania in 1914 upon the death of his uncle. During World War I, he initially maintained Romania's neutrality but later entered on the side of the Allied Powers in 1916. Through Ferdinand's leadership, Romania grew significantly in size by the end of the war to include regions of Bessarabia, Bukovina, and Transylvania. Ferdinand died of cancer in 1927 and was succeeded by his grandson under a regency.