Complex sentence: Degenerate art was legally banned from entering Germany by the Nazis, and once so designated, was held in what was called the Martyr's Room at the Galerie nationale du Jeu de Paume in Paris, France.
Split into simpler sentences: Degenerate art was legally banned from entering Germany by the Nazis. Once so designated, this art was held in what was called the Martyr's Room at the Galerie nationale du Jeu de Paume in Paris, France.