Complex sentence: In July 1915, a Central War Industries Committee, established under the chairmanship of a prominent Octobrist Guchkov, included ten workers' representatives-in which the Petrograd Mensheviks agreed to join despite the objections of their leaders abroad.
Split into simpler sentences: In July 1915, a Central War Industries Committee was established under the chairmanship of a prominent Octobrist, Guchkov, and including ten workers' representatives. The Petrograd Mensheviks agreed to join despite the objections of their leaders abroad.