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 in World War II
Throughout the Antonescu years, Romania supplied Nazi Germany and the Axis armies with oil, grain, and industrial products. Also, numerous train stations in the country, such as Gara de Nord in Bucharest, served as transit points for troops departing for the Eastern Front. Consequently, by 1943 Romania became a target of Allied aerial bombardment. One of the most notable air bombardments was Operation Tidal Wave — the attack on the oil fields of Ploiești on 1 August 1943. Bucharest was subjected to intense Allied bombardment on 4 and 15 April 1944, and the Luftwaffe itself bombed the city on 24 and 25 August after the country switched sides.