Complex sentence: The Xiang Army and Huai Army became the Green Standard Army in 1862 and they raised the third time to surrounded Nanjing until this 14 year long civil war ended in July 1864.
Split into simpler sentences: The Xiang Army and Huai Army became the Green Standard Army in 1862 and they besieged Nanjing. This 14 year long civil war ended in July 1864.