Hungary–Romania relations
During World War II, Hungary and Romania became allies and participated in the war against the Soviet Union. But after the coup on 23 August 1944 Romania switched sides and fought against Hungary. Consequently, Soviet and Romanian troops invaded Hungary, occupied Northern Transylvania by October 1944 and re-established the Romanian administration in the region in March 1945. The 1947 Treaty of Paris reaffirmed the borders between Romania and Hungary as originally defined in Treaty of Trianon 27 years earlier, thus confirming the return of Northern Transylvania to Romania.
Romania's foreign policy in the years preceding the outbreak of the World War I
The Balkan Wars constituted the most severe test of the alliance of Romania with Austria-Hungary. In the Second Balkan War the actions of Romania did not receive any support from the Habsburg Empire, which had as a main objective the assimilation of Bulgaria into the Triple Alliance. In the same time, a warming of the official relationships between Romania and France has produced after France supported and approved the actions of Romania and the terms of the treaty of Bucharest. "The Balkan crisis of 1912–1913 completed the alienation of Romania in relation to Austria-Hungary and the Triple Alliance. [...] In the spring of 1914, the approach between Romania and Triple Entente was a real fact".