Complex sentence: Three years later, after the death of Dior's mother and brother and a financial disaster in the family's fertilizer business, during the Great Depression, that resulted in his father losing control of Dior Frères, the gallery had to be closed.
Split into simpler sentences: Three years later, after the death of Dior's mother and brother and a financial disaster in the family's fertilizer business. During the Great Depression, that resulted in his father losing control of Dior Frères, the gallery had to be closed.