The international peace treaties from 1919-1920, signed at Neuilly, Saint Germain, Trianon and Paris, were instruments to establish new European realities but sanctioned just the same, the union of provinces, inhabited by Romanians, into a whole village, completing the forming of the unitary Romanian state.
The objectives of the foreign policy during the inter-war period, where Nicolae Titulescu played a major role, were aimed at maintaining the territorial status-quo, by creating regional alliances, supporting the League of Nations and the policy of collective security.
At the start of the Second World War, Romania declared itself neutral. The defeats suffered by France and Great Britain created a dramatic situation for Romania, the soviet government forcing Romania, through the ultimatum dated from June 26 and 28, 1940, to yield not only Basarabia, but the north of Bucovina and the land of Herţa as well. Following the Romanian-Bulgarian discussions in Craiova, on September 7, 1940, a treaty was signed, yielding the southern Dobrogea (Quadrilater) to Bulgaria.
The crisis in the summer of 1940 led to Carol II resignation from the crown in his son's favour, Mihai I (September 6, 1940); at the same time, it led to the Government's take over by General Ion Antonescu. With the desire to regain the territories lost in 1940, Ion Antonescu took part with Germany, in the war against the Soviet Union (1941-1944). The losses suffered by the Central Powers, after 1942 led to an increasing number of attempts to remove Romania from its alliance with Germany. On August 23, 1944, Marshal Ion Antonescu was arrested by the order of king Mihai I. The new government, formed out of military men and partisans, declared war to Germany (August 24, 1944).
The Peace Treaty from Paris (February 10, 1947), denied Romania of its status of co-belligerence and compelled it to pay a colossal war compensation; however, the Treaty acknowledged the retrocession of the territories from the north-eastern part of Transylvania to Romania, whilst Basarabia and the northern part of Bucovina remained attached to the URSS. The soviet troops were stationed in Romania and the entire government was taken over through force by communists, political parties were banned, and their members persecuted and arrested; king Mihai I was forced to resign the crown and on the same day, the People's Republic of Romania was declared (December 30, 1947). The dictatorship of a sole party was established, based on an omnipotent and omnipresent surveillance and on the force of repression.
Industrial enterprises, banks and means of transport were nationalized (1948), the agriculture was forcibly collectivized (1949-1962). The entire economy developed according to the five year plans, the main objective being the soviet type of industrialization. Romania became a founding member of the Council for Mutual Economic Assistance (1949) and the Treaty of Warsaw (1955). After the death of Gheorghe Gheorghiu Dej (1965), the communist leader of the post war period, the party leadership, which later was identified as state leadership, was taken by Nicolae Ceauşescu.