Romania's peacetime army was manned by limited conscription, and all adult males spent time in the territorial reserve. This gave it a regular strength of around 100,000 men. On the outbreak of the Second Balkan War in 1913, conscription was introduced and the army grew to 400,000.

In August 1916, Romania joined the Allies against the Central Powers. Within weeks Germany responded by invading Romania and by the end of the year controlled Wallachia and Dobrudja and most of the country's natural resources including its oil supplies.

After Russia withdrew from the fighting Romania was placed in an impossible situation and in December, 1917, the prime minister announced a ceasefire. Under the Treaty of Bucharest, Romania became a virtual economic colony of the Central Powers. Germany stripped the country of food and raw materials and it is estimated that the occupation led to the deaths of 500,000 civilians.