Short answers, pulled from the story.
The Second Vienna Award was a territorial arbitration signed on the 30th of August 1940, by which Germany and Italy assigned 43,104 square kilometers of northern Romania to Hungary. It transferred a region with a mixed Romanian and Hungarian population without resolving the underlying ethnic distribution, leaving between 1,150,000 and 1,300,000 Romanians inside the newly Hungarian-controlled territory.
Hungary held Northern Transylvania from September 1940 to October 1944, roughly four years. The first Hungarian military unit crossed the border at Sighetul Marmației on the 5th of September 1940, and the last Hungarian and German troops were defeated at the Battle of Carei on the 25th of October 1944.
Excluding the Szekely area, 127,377 Jews were deported from Northern Transylvania to the Auschwitz death camp. Of those, 19,764 returned after the war; 107,613 did not return. The deportations were carried out in 1944 following the German occupation of Hungary in March of that year.
The Treznea and Ip massacres were killings of Romanian civilians that occurred in the first weeks after Hungary took control of Northern Transylvania in September 1940. A Romanian statistical report covering August 1940 to November 1941 recorded 919 murders in the territory overall. Survivor Gavril Butcovan, from Ip commune in Sălaj, also testified that some local Hungarians risked their lives to protect Romanian families during these events.
Romanian administration returned to Northern Transylvania on the 10th of March 1945, after being expelled by Soviet forces in November 1944 due to Romanian paramilitary activity. The 1947 Paris Peace Treaty formally confirmed the region's return to Romania by reaffirming the borders originally set by the Treaty of Trianon in 1920.
The 1930 Romanian census recorded a total population of 2,393,300, with Romanians at about 49 percent and Hungarians at about 38 percent by nationality. The 1941 Hungarian census, conducted after the transfer, registered 2,578,100 people and showed Hungarians at roughly 54 percent and Romanians at about 40 percent by nationality. The differences reflected migration, Jewish assimilation into Hungarian counts, and the departure of over 100,000 Romanian refugees.