What incident sparked the outbreak of the Second Sino-Japanese War in 1937?

The incident that sparked the Second Sino-Japanese War in 1937 was the Marco Polo Bridge Incident. On July 7, 1937, a confrontation between Chinese and Japanese troops near the Marco Polo Bridge, outside Beiping (now Beijing), escalated into full-scale warfare. This conflict marked the beginning of the Second Sino-Japanese War, which lasted until 1945 and was a prelude to the Pacific theater of World War II. The incident occurred amidst growing Japanese expansionism in China and a unified Chinese resistance movement formed by the Nationalists and Communists.1234