Following the war, Horthy retired. He soon entered politics as the leader of the conservative White forces against the communist government of Béla Kun. On 1 March 1920, Horthy became regent of Hungary and head of the executive authority. At first Horthy had little power, but his power increased sharply after 1937 when he refused to be bound by decisions of the Hungarian Parliament.
In domestic policy, Horthy rejected universal and secret suffrage and land reform. In foreign policy, his chief aim was revision of the Treaty of Trianon of 1920, by which Hungary had lost two-thirds of its territory and population. For this reason, although he was strongly anti-Fascist, Horthy sought the support of, and an alliance with, Germany and Italy. His diplomatic efforts were successful in that between 1938 and 1940, Hungary recovered some of the territory it had lost after World War I to Czechoslovakia, Romania, and Yugoslavia.
Horthy successfully managed to afford involvement in the war in September 1939. By April 1941, however, pressure from Adolf Hitler, coupled with promises of additional territory and access to the Adriatic, led to Hungarian military operations against Yugoslavia on the Axis side. Horthy was also forced to send troops to fight on the Eastern Front against the Soviet Union, but he resisted German efforts to have him deport Hungarian Jews.
In 1943, Horthy was already considering escaping from Hitler's grasp and negotiating with the Allied powers. Aware of this activity and determined to keep Hungary in the war on his side, Hitler sent German troops to occupy the country on 19 March 1944. Horthy remained in his post. In September, Soviet troops invaded Hungary from Romania, and on 28 September Horthy dispatched representatives to Moscow. There they signed a preliminary armistice agreement on 11 October, which Horthy announced publicly four days later. A lack of coordination with army chief of staff General János Vörös led to a continuation of the fighting. The German army then occupied Budapest and took Horthy's son hostage, forcing Horthy to appoint Ferenc Szálasi, head of the German Arrow Cross (Fascist) Party, as "Leader of the Nation."
The Germans then removed Horthy to Bavaria, where he was captured by the Americans. In 1946, Horthy appeared as a witness at the postwar International Military Tribunal at Nuremberg. The Yugoslav government requested his extradition so that he might be tried there for war crimes, but the U.S. authorities refused the request. Horthy then moved to Portugal, where he remained. The Soviet occupation and subsequent communist government of Hungary made it impossible for him to return there. Horthy wrote his memoirs in 1953, but they were not published in Hungary until 1990. He died in Estoril, Portugal, on 9 February 1957. In 1993, following the departure of the last Soviet soldiers from Hungary, Horthy's remains were reburied in Kenderes, Hungary.
Benesik, Gábor. Alexander Horthy: The Governor and His Era. Budapest: Magyar Mercuaius, 2001.; Horthy, Miklós. Memoirs. New York: R. Speller, 1956.; Vígh, Károly. "A kormányzó országlásának a vége. 1944. Október 15" [End to the governor's power: 15 October 1944]. Élet és Tudomány 49 (1994): 1262–1264.