During his first ten years, Horthy led increased repression of Hungarian minorities. In 1920, the "numerus clausus" law formally placed limits on the number of minority students at university, and legalized corporal punishment for adults in criminal cases. Although the law seemingly applied in equal measure to all minorities, the ethnicity quota system was never fully introduced and the law acted largely to conceal anti-Jewish action from foreign observers. Limitations were relaxed in 1928. Racial criteria in admitting new students were removed and replaced by social criteria. Five categories were set up: civil servants, war veterans and army officers, small landowners and artisans, industrialists, and the merchant classes. Under István Bethlen as Prime Minister the electoral system was changed to reintroduce an open vote system outside Budapest and its vicinity and cities with county municipal rights. Bethlen's political party, the Party of Unity, won repeated elections. Bethlen pushed for revision of the Treaty of Trianon. After the collapse of the Hungarian economy from 1929 to 1931, national turmoil pushed Bethlen to resign as Prime Minister. In 1938 the changes to the electoral system were reversed.