Answer:
The Second Sino-Japanese War began on July 7, 1937, with the Marco Polo Bridge Incident. This incident involved a dispute between Chinese and Japanese troops near the Marco Polo Bridge in Beijing, which escalated into a full-scale invasion of China by Japan.
The Japanese had been expanding their empire and seeking to establish greater control over China for several years prior to the Marco Polo Bridge Incident. They had previously invaded Manchuria in 1931, and established a puppet state there called Manchukuo. They also sought to establish control over other parts of China through various means, including economic dominance and political influence.
The Marco Polo Bridge Incident provided Japan with the pretext it needed to launch a full-scale invasion of China. The conflict quickly spread throughout China, with the Chinese putting up fierce resistance against the Japanese aggression. The war lasted for eight years, until Japan's surrender in 1945 at the end of World War II.