Task: Question Generation
Input (English): Passage: The Kingdom of Hungary , also known as the Regency, existed from 1920 to 1946 as a de factonote 1 country under Regent Miklós Horthy. Horthy officially represented the Hungarian monarchy of Charles IV, Apostolic King of Hungary. Attempts by Charles IV to return to the throne were prevented by threats of war from neighbouring countries and by the lack of support from Horthy. The country has been regarded by some historians to have been a client state of Germany from 1938 to 1944. The Kingdom of Hungary under Horthy was an Axis Power during most of World War II.  In 1944, after Horthy's government negotiated secretly with the Allies, and considered to leave the war as well, Hungary was occupied by Nazi Germany and Horthy was deposed. The 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, Hungary fell within the Soviet Union's sphere of interest. In 1946, the Second Hungarian Republic was established under Soviet influence. In 1949, the communist Hungarian People's Republic was founded.
Output (English): What stopped Charles IV from returning to the throne?