Complex sentence: When Chief commander Zhang Guoliang and Imperial Commissioner Her Chyun died the Qing government promoted Zeng Guofan which changed the course of the war in favor of the Qing and their western allies.
Split into simpler sentences: When Chief commander Zhang Guoliang and Imperial Commissioner Her Chyun died the Qing government promoted Zeng Guofan. This changed the course of the war in favor of the Qing and their western allies.