Humani generis unitas

Humani generis unitas (Latin; English translation: On the Unity of the Human Race) was a draft for an encyclical planned by Pope Pius XI before his death on February 10, 1939. The draft text condemned antisemitism, racism and the persecution of Jews. Because it was never issued, it is sometimes referred to as "The Hidden Encyclical" or "The Lost Encyclical." Humani generis unitas was written by three Jesuits under the leadership of John LaFarge. The draft text remained secret until published in 1995 in France (by Passelecq and Suchecky under the title L’Encyclique Cachée de Pie XI) and in 1997 in English as The Hidden Encyclical of Pius XI.

In June 1938, Pius XI assigned American Jesuit John LaFarge to prepare a draft of Humani generis unitas. Jesuit Superior-General Wlodimir Ledóchowski assigned two other Jesuits, Gustav Gundlach and Gustave Desbuquois, to assist LaFarge. Working in Paris, they produced a draft of approximately 100 pages. Another Jesuit translated the draft into Latin and presented it to Ledóchowski. The draft was delivered to the Vatican in September 1938.

Some secondary sources, including Cardinal Tisserant, claim that the draft was on Pius XI's desk when he died of a heart attack on February 10, 1939.

Pius XI's successor, Pope Pius XII, did not promulgate the draft as an encyclical. Critics of Pius XII (notably John Cornwell in his controversial work Hitler's Pope) cited this decision as evidence of his alleged silence toward anti-Semitism and The Holocaust. He utilized parts of it in his own inaugural encyclical Summi Pontificatus on the unity of human society, in October 1939, the month after the outbreak of World War II, and analysis of the draft figures prominently in most comparisons of the policies of Pius XII and his predecessor.

...
Wikipedia