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.
Carol II of Romania
When World War II began with the German and Soviet invasion of Poland on 1 September 1939, followed up by British and French declarations of war on Germany on 3 September 1939, Carol proclaimed neutrality. In doing so, Carol violated the letter of the treaty of alliance with Poland signed in 1921 and the spirit of treaty of alliance signed with France in 1926. Carol justified his policy on the grounds that neutrality provided the only hope of preserving the independence of Romania in light of the alliance between Germany and the Soviet Union established in the Molotov–Ribbentrop Pact of August 1939 and French unwillingness to mount an invasion of Germany. As usual with Carol, he sought to play a careful balancing act between competing major powers, on one hand signing a new economic treaty with Germany, while on the other hand allowing for a considerable period of time for the Polish troops to cross into Romania without interning them, as international law required. The Poles instead were allowed to travel to Constanța to board ships to take them to Marseille to continue the fight against Germany from France. The Romanian Bridgehead remained a key escape route for thousands of Poles in the desperate days of September 1939. It was only after receiving a number of furious complaints from Fabricius about the passage of Polish soldiers across Romania that Carol finally started to intern the fleeing Poles.