How did the unification of the Romanians in 1918 come about?

The reason was Romania’s participation in the First World War. The first years she hesitated on which side to speak – the Entente or the Central Powers. In the military leadership of Russia, it was treated with disdain in the style of “It will take 30 divisions to defeat it or protect it in case of entering the war.” Influenced by the success of the Brusilov breakthrough, Romania declared war on Austria-Hungary, Bulgaria and Germany in August 1916, but was quickly defeated. The Romanians surrendered Bucharest and Ploiesti with its oil fields. By the beginning of 1917, the front had stabilized thanks to the participation of the Russian army. This continued until December 1917. Until Romania went over to the side of Germany and seized Bessarabia, Bukovina and Budzhak, and at the end of 1918 she again went over to the side of the Entente and seized Transylvania. Thus, by the beginning of 1919, its new boundaries were formed.