Timeline of China's resistance against Japanese aggression

During special commemorations in 2015, Chinese President Xi Jinping said: "The great contributions made by the Chinese people to the world's anti-fascist war should be remembered ... We must cherish peace and create a better future." 
Japan had troops in China since the beginning of the 20th century, long before the war began. But when it did invade in the 1930s, China was largely a weak and rural country struggling with civil war, social unrest and a poor economy.