Complex sentence: This effort ultimately failed, and in July and August 1920 Ternopil was captured by the Red Army in the course of the Polish-Soviet War and served as the capital of the Galician Soviet Socialist Republic.
Split into simpler sentences: This effort ultimately failed, and in July and August 1920 the Red Army captured Ternopilin the course of the Polish-Soviet War. The city then served as the capital of the Galician Soviet Socialist Republic.