Hypothesis Z (Romanian: Ipoteza Z), sometimes known as Plan Z (Romanian: Planul Z), was the name of Romania's first war plan for World War I. It was based on an offensive against the Austro-Hungarian Empire in Transylvania and a simultaneous defense of the country against Bulgarian attacks in the south. Once Russian forces arrived in Dobruja, the Romanian Army would launch another offensive against Bulgaria. Hypothesis Z was definitively developed and completed by July 1916. Its application in the war, in which Romania entered in August 1916, was unsuccessful, but its main objective, to achieve the unification of the Romanian nation, was realized anyway after the war.