Complex sentence: However, a sortie from the Astrakhan garrison drove back the besiegers--a Russian relief army of 15,000 attacked and scattered the workmen and the Tatar force sent for their protection.
Split into simpler sentences: However, a sortie from the Astrakhan garrison drove back the besiegers. A Russian relief army of 15,000 attacked and scattered the workmen and the Tatar force sent for their protection.