Complex sentence: In February 1902, Kuprin married Maria Karlovna Davydova, the adopted daughter of Alexandra Davydova, the widow of the Saint Petersburg Conservatory's director who, after her husband's death in 1889, became editor of "Mir Bozhy".
Split into simpler sentences: In February 1902, Kuprin married Maria Karlovna Davydova, the adopted daughter of Alexandra Davydova, widow of the director of the Petersburg Conservatoire. On her husband's death in 1889, Alexandra Davydova became editor of "Mir Bozhy".