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.
Romanian Volunteer Corps in Russia
During 1916, Romania entered World War I as an Entente country, in alliance with the Russian Empire against Austria-Hungary and the other Central Powers. After a while, Romania began investigating the fate and loyalties of Austria-Hungarian Romanians who were held in Russian POW camps. Estimates for that period place the total population of Bukovinan and Transylvanian Romanians in such facilities, throughout Russia, at 120,000 or 130,000. Meanwhile, in Romania itself there were several thousand Romanian refugees from Austria-Hungary who immediately signed up for service in the Romanian Armed Forces.