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.
First Army (Romania)
The last offensive the First Army took part in World War II was the Prague Offensive in May 1945. During the Prague Offensive, the First Army operated together with the Romanian Fourth Army as part of the Soviet 2nd Ukrainian Front. Marshal Ivan Koniev, the commander of the First Ukrainian Front, was the main Soviet commander in the area. Together with Marshal Georgy Zhukov's First Byelorussian Front, Koniev had launched the great attack on April 16 that resulted in the fall of Berlin and Soviet victory on the Eastern Front.