hosts POW invalided out of military service from Entente and Central Powers During the war Switzerland accepted 68,000 British, French and German wounded prisoners of war for recovery in mountain resorts. To be transferred the wounded had to have a disability that would negate their further military service or have been interned over 18 months with deteriorating mental health. The wounded were transferred from prisoner of war camps unable to cope with the number of wounded and sat out the war in Switzerland. The transfer was agreed between the warring powers and organised by the Red Cross. Interwar period One potential result of World War I was an expansion of Switzerland itself during the Interwar period. In a referendum held in the Austrian state of Vorarlberg on 11 May 1920, over 80% of those voting supported a proposal that the state join the Swiss Confederation. However, this was prevented by the opposition of the Austrian Government, the Allies, Swiss liberals, the Swiss-Italians and the Swiss-French. However, the Principality of Liechtenstein managed to exclude itself from Austria in 1918 and signed a monetary and customs union with Switzerland that effectively guaranteed its independence. In 1920, Switzerland joined the League of Nations. In 1934 the Swiss Banking Act was passed. This allowed for anonymous numbered bank accounts, in part to allow Germans (including Jews) to hide or protect their assets from seizure by the newly established Third Reich. In 1936 Wilhelm Gustloff was assassinated at Davos; he was the head of the Nazi Party's "Auslands-Organisation" in Switzerland. The Swiss government refused to extradite the alleged assassin David Frankfurter to Germany. Frankfurter was sentenced to 18 years in prison but was pardoned in 1946. As European tension grew in the 1930s, the Swiss began to rethink their political and military situation. The Social Democratic party abandoned their revolutionary and anti-military stances, and soon the country began to rearm for war. BGB Federal Councillor Rudolf Minger, predicting war would come in 1939, led the rebuilding of the Swiss Army. Starting in 1936, he secured a larger defence budget and started a war bond system. The army was restructured into smaller, better equipped divisions and boot camp for conscripts was extended to 3 months of instruction. In 1937 a war economy cell was established. Households were encouraged to keep a two-month supply of food and basic necessities. In 1938 Foreign Minister Giuseppe Motta withdrew Switzerland