After the July 7 Incident in 1937, Japan launched a full-scale invasion of China, igniting the Chinese people's War of Resistance Against Japanese Aggression. With superior weapons and tactics, Japanese forces quickly took Beijing and Tianjin before advancing deep into north China. But in a narrow mountain valley in Shanxi, their overconfidence cost them dearly as the poorly equipped Eighth Route Army dealt a heavy blow. How did the Chinese soldiers achieve such a remarkable victory? Click the video to find out.