Complex sentence: Before the 1917 Revolution the Mikhailovsky did not have its own resident company: performances were given either by a French company, hired by the Russian Imperial Theatres, or at the end of the century by the Mariinsky Theatre and Alexandrinsky Theatre companies.
Split into simpler sentences: Before the 1917 Revolution, the Mikhailovsky did not have its own resident company. Performances were given either by a French company, hired by the Russian Imperial Theatres or at the end of the century by the Mariinsky Theatre and Alexandrinsky Theatre companies.