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.
History of Romania
During the war, Romania was the most important source of oil for Nazi Germany, prompting multiple bombing raids by the Allies. By means of the Axis invasion of the Soviet Union, Romania recovered Bessarabia and northern Bukovina from the Soviet Russia, under the leadership of general Ion Antonescu.
The Antonescu regime played a major role in the Holocaust, following to a lesser extent the Nazi policy of oppression and massacre of the Jews and Romas, primarily in the Eastern territories Romania recovered or occupied from the Soviet Union (Transnistria) and in Moldavia. According to an international commission report released by the Romanian government in 2004, Antonescu's dictatorial government of Romania was responsible for the murder in various forms including deportations to concentration camps and executions by the Romanian Army and Gendarmerie and the German Einsatzgruppen of some 280,000 to 380,000 Jews on Romanian territories and in the war zones of Bessarabia, Bukovina and Transnistria.