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.
Romanians
During World War II, the Kingdom of Romania lost territory both to the east and west, as Northern Transylvania became part of Hungary through the Second Vienna Award, while Bessarabia and northern Bukovina were taken by the Soviets and included in the Moldavian SSR, respectively Ukrainian SSR. The eastern territory losses were facilitated by the Molotov-Ribbentrop German-Soviet non-aggression pact.