The Kingdom of Romania formally declared war on Austria-Hungary, marking its entry into World War I on the side of the Allied Powers. The roots of this decision can be traced back to Romania's aspirations for territorial expansion and national unity, particularly regarding Transylvania, a region populated predominantly by ethnic Romanians but ruled by Austria-Hungary. The declaration followed a period of diplomatic maneuvering and promises of support from the Allies, including Russia, which played a crucial role in encouraging Romania to join the fight against the Central Powers.

The Romanian military mobilized with enthusiasm, eager to reclaim Transylvania and fulfill nationalistic ambitions. However, Romania was not fully prepared for the extensive warfare that was about to unfold. As Romanian troops launched offensives into Transylvania, they initially met some success, bolstered by support from Russian forces. However, the military strategy quickly turned challenging, as the Central Powers launched counteroffensives, leading to significant setbacks for Romania.

Romania's entry into the war not only shifted the balance of power on the Eastern Front but also demonstrated the complex layer of national interests and alliances during the war. Furthermore, Romania's involvement ultimately did not turn out as hoped, as it would face occupation by Central Powers forces, leading to devastating impacts on its economy and society.