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.
Social Democratic Party of Romania (1910–18)
The party's anti-militarist stance led it to condemn both Romania's participation in the Second Balkan War and, after the start of World War I, the "social patriotic" stance of Western social-democratic parties. Accordingly, it proposed a federalist solution for the complicated ethnic situation in the Balkans, and, after some internal debates, joined the Zimmerwald movement. Neutral at first, by 1916 Romania's government was increasingly open to participation in the war on the Entente side, and decided to crack down on the socialist movement, brutally repressing a pacifist demonstration in Galați in June. The PSD was banned outright when the country declared war on the Central Powers later that year.