The chief Hungarian foreign policy objective between the two world wars was revision of the 1920 Treaty of Trianon. Virtually all Hungarians saw the treaty as a national humiliation. It had destroyed the economy and national territorial integrity of Hungary by stripping away some two-thirds of the territory and population. It also consigned 3 million Hungarians to foreign rule. Revisionist sentiment meant the Horthy government fell easy prey to German promises of territorial aggrandizement if Hungary joined the Axis. As a result of the Munich Conference and First Vienna Decision in the autumn of 1938, the German occupation of Czechoslovakia on 15 March 1939, and the Second Vienna Decision in August 1940, Hungary received some of the territories lost after World War I without having to take part in any military operations. Hungary's new alliance with Italy and especially with Germany seemed to be working to the nation's advantage. In return, Hungary provided Germany with increasing amounts of raw materials and food. During the war, Hungary also emerged as a major source of oil for the Reich, ultimately surpassed only by Romania.
In December 1940, the Hungarian government concluded a friendship agreement with Yugoslavia. A few months later, however, Adolf Hitler decided to attack Yugoslavia, and he insisted that Hungary participate in the military operations. Rather than dishonor himself with such an act, Hungarian Prime Minister Pál Teleki committed suicide. Regent Horthy, new Prime Minister László Bárdossy, and chief of staff of the army General Henrik Werth were all committed to Hungarian participation in the invasion of Yugoslavia. They hoped in the process to gain additional territory and cement the alliance with Germany. Hungary entered the war on 11 April 1941.
When Germany invaded the Soviet Union in June 1941, it called on Hungary to participate fully in the war effort. Hungary suspended diplomatic relations with the Soviet Union, and on 27 June, after a northern Hungarian city was bombed by aircraft identified as Soviet (but which were in fact of unknown origin), Hungary declared war on the Soviet Union. Hungarian army leaders expected a rapid German victory over the USSR.
By the end of June, Hungarian troops were deployed on the Eastern Front. Hungarian forces were split: offensive units advanced with German forces into Soviet territory, and an occupying force provided security for the German rear areas. Much to its chagrin, Hungary ultimately found itself at war with Britain and the United States. The United States declared war on Hungary on 5 June 1942.
In January 1942, under heavy German pressure, Bárdossy promised to send additional troops to the Eastern Front. On 9 March 1942, largely because the Germans had failed to secure a quick victory over the Soviets, Horthy replaced Bárdossy as prime minister with Miklós Kállay. The new prime minister sought to continue his predecessor's policy of open cooperation with Germany while also conducting secret negotiations with the Anglo-Saxon powers in the hope of extricating Hungary from the war.
Meanwhile, between April and June 1942, the Second Hungarian Army of 200,000 men was sent to the Eastern Front to bolster German forces there. Hungarian forces in the Soviet Union suffered from obsolete and insufficient equipment, poor logistics, and insufficient ammunition. The tragic defeat of the Second Hungarian Army near Voronezh in the Battle of the Don River during the winter of 1943 was a catastrophe for Hungary that resulted in the deaths of some 120,000 troops.
Following this loss, Kállay was more determined than ever to extricate Hungary from the war. His secret diplomacy intensified even as Hungarian participation in military operations was being curtailed. This angered Hitler, who demanded nothing less than full Hungarian participation in the war. Hitler was also upset by secret Hungarian negotiations with the western Allies to withdraw from the war, an activity about which pro-German individuals within the Budapest government kept him well-informed.
Alarmed by the Hungarian government's attempts to leave the war, on 19 March 1944 Hitler sent in German troops to occupy the country and force its continued participation on the German side. Under German pressure, Horthy also appointed Döme Sztójay, a pro-German former Hungarian ambassador to Berlin, as the new prime minister. Anti-Nazi parties were banned, and politicians opposed to German policy were arrested. The Hungarian government was also forced to deploy additional soldiers to the Eastern Front to fight against the Soviets. One irony of the German occupation was the reduced economic value of Hungary to the Reich, thanks to the occupation costs, the mass arrest and deportation of Jews, and increased Allied bombing.
In an attempt to decrease German influence, on 29 August 1944 Horthy appointed a new prime minister, Géza Lakatos, who ordered Hungarian army units to attack southern Transylvania to halt a Soviet-Romanian invasion. Understanding that the war was lost, Horthy dispatched a delegation to Moscow to negotiate an armistice with the Soviet Union, the terms of which were agreed to on 11 October 1944.
On 15 October 1944, Horthy announced over the radio Hungary's unconditional surrender. Because of a lack of coordination with army chief of staff János Vörös, the Hungarian army continued to fight, and Horthy's attempt at surrender failed. The Germans then took over Budapest and forced Horthy to step aside in favor of Ferenc Szálasi, leader of the Arrow Cross (the Hungarian fascist party) as prime minister and head of state. Horthy was then arrested by the Gestapo and removed to Germany with his family. During Szálasi's brief tenure, a reign of terror swept Hungary. Thousands of people, including many Jews who had sought refuge in Budapest, were arrested and executed or sent to concentration camps.
Meanwhile, the Soviet army continued to advance, and by December 1944 it laid siege to Budapest. Two and a half months later, the remaining German forces in Buda surrendered. Meanwhile, Hungarian representatives signed an armistice in Moscow on 20 January 1945. Most fighting in the country ended in February 1945, and the last German troops were forced from Hungarian soil on 13 April 1945. The country then passed from German to Soviet army control.
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