The Hungarian air force attacks the headquarters of the Slovak air force in Spišská Nová Ves, killing 13 people and beginning the Slovak-Hungarian War.

The Slovak Air Force (Slovak: Slovensk vzdun zbrane, or SVZ), between 1939 and 1945, was the air force of the short-lived World War II Slovak Republic. Its mission was to provide air support at fronts, and to protect Bratislava and metropolitan areas against enemy air attack.

The Kingdom of Hungary (Hungarian: Magyar Királyság), sometimes referred to as the Regency or the Horthy era, existed as a country from 1920 to 1946 under the rule of Regent Miklós Horthy, who nominally represented the Hungarian monarchy. In reality there was no king, and attempts by King Charles IV to return to the throne shortly before his death were prevented by Horthy.

Hungary under Horthy was characterized by its conservative, nationalist and fiercely anti-communist character. The government was based on an unstable alliance of conservatives and right-wingers. Foreign policy was characterized by revisionism — the total or partial revision of the Treaty of Trianon, which had seen Hungary lose over 70% of its historic territory along with over three million Hungarians, who mostly lived in the border territories outside the new borders of the kingdom. Hungary's interwar politics were dominated by an obsession with the territorial losses suffered in this treaty, with the resentment continuing until the present.

Germany's influence in Hungary has led some historians to conclude that the country increasingly became a Nazi client state after 1938. The Kingdom of Hungary was an Axis Power during World War II, intent on regaining Hungarian-majority territory that had been lost in the Treaty of Trianon, which it did in early 1941. By 1944, following heavy setbacks for the Axis, Horthy's government negotiated secretly with the Allies, and also considered leaving the war. Because of this Hungary was occupied by Germany and Horthy was deposed. The extremist Arrow Cross Party's leader Ferenc Szálasi established a new Nazi-backed government, effectively turning Hungary into a German-occupied puppet state.

After World War II, the country fell within the Soviet Union's sphere of influence. It changed its name to the Hungarian State (Hungarian: Magyar Állam) and the Second Hungarian Republic was soon thereafter proclaimed in 1946, succeeded by the communist Hungarian People's Republic in 1949.