The Jewish-born Roman Catholic convert Czech composer Viktor Ullmann's Der Kaiser Von Atlantis was his last composition in the Terezin concentration camp outside Prague before he was shipped to Auschwitz in 1944 and gassed on arrival.
One of the remarkable stories of the era is about all of the music in the camps, and Terezin had more than its share of talent. The Nazis and even the SS loved music and thus encouraged camp musicianship. Mrs. BD recently heard a Terezin survivor speak about being in the choir there at age 11. (140,000 passed through Terezin: 20,000 were liberated at the end.)
In this short (50+ min.) modernist opera, the Emperor of Atlantis (a thinly-disguised Hitler-type) declares total war on the world. (As one would expect from a prison camp opera, the "Loudspeaker" has a major role and, instruments being limited, it's like a cabaret band.) Death goes on strike out of resentment at the competition from the Emperor, but love reappears on the battlefield and, in the end, Death is persuaded to resume his merciful task of erasing pain from the world when the emperor himself agrees to die.
Here's a snippet of the opera on YouTube, the Emperor's farewell aria: