Complex sentence: After its Second Congress the OSR's Soviet was chaired by Vladimir Yudovsky who was installed after a pro-Bolshevik coup d'état organized by the Narkom Nikolai Krylenko.
Split into simpler sentences: After its Second Congress, the OSR's Soviet was chaired by Vladimir Yudovsky. He had been installed after a pro-Bolshevik coup d'état organized by the Narkom Nikolai Krylenko.