Nazi Germany is probably the most well-known, 20th century, case of mass censorship. The custom of mass book burnings and persecution of people with ideas that did not agree with Nazi philosophy first began on April 6, 1933 with a proclamation released by the German Students Association for Press and Propaganda. They urged the “cleansing” of literature and threw public festivals to celebrate the bonfires. On May 10, 1933, the largest of these book burnings took place. University students burned around 25,000 copies of literature deemed “un-German”. Books written by Jewish, communist, and socialist authors were burned in huge bonfires. Select authors such as Ernest Hemmingway and Jack London, Helen Keller, Sigmund Freud, and Upton Sinclair also had their works find their way into the Nazi fires. Stalin, leader of the USSR, also in an effort to abolish Jewish culture, ordered the burning of Jewish books in his country in the 1930’s and 1940’s.